World number one van Gerwen had looked set to cruise through to the last 16 at the Citywest Hotel when he took the opening set without reply against the World Youth Champion and also led by a leg in the second set.
Isle of Wight youngster Brown hit back with three successive legs to send the game into a third set, and then took out a superb 152 finish to level in the decider - but van Gerwen sealed victory with legs of 13 and 14 darts to progress.
"My doubles were good in the first set but then my level dropped and I put myself under pressure, but Keegan put me under pressure too in that second set," said van Gerwen, who landed five 180s.
"I let myself down in the second set and that shouldn't happen, especially in a format like this, but it's nice to know that I've got an extra gear and I played a fantastic last set.
"My confidence is good and I want to defend my title."
Belgium's Kim Huybrechts won his first game at the World Grand Prix in four attempts as he came from a set down to defeat Benito van de Pas with six straight legs as he swept into the last 16.
Huybrechts led 2-1 in the opener, only to see van de Pas punish three missed set darts by finishing 100 to claim the lead, and the Dutch debutant also led in the second.
Huybrechts responded superbly, levelling on double 16 before finishing 84 and 109 - for a 12-darter - to take the set before then finishing 76 and 117 to move 2-0 up in the third set as double two for the next leg sealed a second round clash with van Gerwen.
"I've been here three times before and never won a set, and I was so nervous tonight," admitted Huybrechts. "It's a big relief and we were both struggling a bit and thinking about the game, but I was strongest in the end.
"I'm a power scoring player and I'm a bit dodgy on doubles sometimes - and you need two doubles to win games here and that makes it even harder for players like me!
"The first one to win in every tournament is the hardest one, so I'm going to relax now. I'll practice a bit on my doubles to get them sharper and I'll be ready for Michael."
Dave Chisnall won the night's most dramatic clash as he escaped from four missed match darts from Peter Wright to snatch victory from the jaws of defeat.
Wright edged a tight opening set 3-2 after Chisnall missed two darts at double 12 in the fifth leg to claim the lead, only for the 2013 Dublin runner-up to take the second set 3-1 to level.
Wright moved 2-0 up in the decider, but missed the bull for the match in leg three and the saw Chisnall finish a 13-darter to send the game into a sudden-death leg.
Wright landed a 180, but missed three more match darts to allow the Premier League semi-finalist in to take out 60 on tops to claim a narrow triumph.
"It was very hard and I had to keep battling," said Chisnall. "I gave him that first set by missing the double 12 and I had to dig in, but I won and I'm happy with that.
"Peter was quite good with his doubles and I didn't think he'd miss at the end, but it was always going to go to the wire."
Chisnall now plays Jelle Klaasen in round two, after the Dutchman knocked out Northern Ireland's Brendan Dolan by coming from a set down to win 2-1.
Dolan, the 2011 World Grand Prix runner-up, took the opening set 3-1, but Klaasen finished 100 and 108 as he won the second set by the same scoreline and then took the final set 3-1 - despite a 125 checkout from his opponent - to progress.
Klaasen has won two Players Championship events this year in his push towards the top 16, and he said: "I've been playing well in the last few months but on TV it's not there yet. I know it will come and maybe this is the beginning.
"I'm very happy and I feel confident. In the first set I missed too many doubles but I was opening well and I felt confident that I could win the game and I'm happy with the way I played.
"It's difficult to play against Brendan but Dave has the same rhythm as me and I hope if I can keep opening like this that I'll have a good chance to win. We're both playing well in the floor tournaments so I hope we can show it on stage."
Number eight seed Michael Smith overcame two missed match darts from Gerwyn Price before claiming a dramatic sudden-death leg win over the Welshman.
Price, on his World Grand Prix debut, kicked off the game with a 160 opening score and won the first set 3-1, but Smith hit back from a leg down in the second to level the game with two 14-darters and also found himself behind in the decider.
Price led 2-0 in set three, with Smith hitting back with a 100 finish before capitalising on two misses from the Welsh ace - at double top and ten - to send the game into a one-leg shoot-out which he claimed on double 14 with a whitewash as his opponent missed 15 starting doubles.
"I didn't get going but Gerwyn let me in and I took my chances," said Smith. "I've played a lot better here and lost, so to get the win I'm happy because I've never won here before.
"During the game I felt like I was playing like the world number 100, but I kept telling myself that I'm the world number eight and to start playing like that, and I battled through where two years ago I'd have lost this game.
"I'm into the last 16 for the first time and it's the business end of the tournament. I've not proven myself on TV yet so that's my focus now."
Smith will now meet another Welshman, youngster Jamie Lewis, in the second round on Tuesday after the Cardigan-based thrower saw off Ireland's William O'Connor 2-1 in another game which went all the way.
Despite the home favourite opening with a 13-darter, Lewis took the first set 3-1 before O'Connor hit back to take the second by the same scoreline.
Lewis led 2-1 in the third before missing two match darts at tops as O'Connor forced a decider, only to then miss two match darts of his own to allow the youngster back in on double five to finally take victory.
"It was a very close game and, after winning the first set, it was closer than I'd expected," admitted Lewis. "Going into that last leg I thought I was gone, but I put myself back in with a chance and managed to get the job done in the end.
"I'm chuffed to win that and I've been playing well, so if I can keep this up then you never know what will happen. I'll take each game as it comes and try to get as far as I can."
Welsh left-hander Mark Webster held off Stephen Bunting's fightback with a superb deciding set as he moved into the second round with a 2-1 up.
Webster - who is battling to maintain his top 32 status - came from a led down to win the opening set 3-1 before Bunting found top gear to win the second set in a deciding leg, despite finding himself 2-1 down at one stage.
The left-hander, though, took out 70 and 104, for a 12-darter, to move 2-0 up in the deciding set, before punishing Bunting's missed doubles by firing in tops for the win.
"I really enjoyed that," said Webster. "It was a big game but I've never lost to Stephen before and I was confident and I thought I did okay.
"Stephen missed too many doubles but when he got back to one set all and it was big, mentally, to get back on top and knock the stuffing out of him in the final set.
"I'm in the last 16 and I'm really pleased."
Webster now meets the number five seed Adrian Lewis, who enjoyed a comfortable straight sets win over two-time World Grand Prix finalist Raymond van Barneveld, who took only one leg in the game.
The Dutchman missed 18 starting doubles in the opening leg as Lewis took the lead, and though van Barneveld posted a 180 in the second it was his opponent who hit tops for a 2-0 lead.
Van Barneveld replied on double eight, but double ten gave Lewis the set before he swept through set two without reply, landing a 177 score and a 180 as he moved into the last 16.
"It's a hard format, no matter who you play, I'll take a 2-0 win over Ray," said Lewis, the 2010 runner-up at the Citywest Hotel. "I've been putting a lot of work in and I started quite brightly."
The first round concludes on Monday night with the remaining eight matches, including 11-time World Grand Prix winner Phil Taylor up against Vincent van der Voort and World Champion Gary Anderson's all-Scottish battle with John Henderson.
Two-time World Grand Prix champion James Wade takes on Austria's Mensur Suljovic, while former finalists Mervyn King and Terry Jenkins also clash.
Australian star Simon Whitlock opens the night against Andrew Gilding, while Justin Pipe meets Steve Beaton, Ian White plays Jamie Caven and Robert Thornton takes on Northern Ireland's Daryl Gurney.
Tickets for the partypoker.com World Grand Prix are available from the Citywest Hotel ny email email@example.com or by calling 01 401 0505 (Outside Ireland 00353 1 401 0505).
partypoker.com World Grand Prix
Sunday October 4
William O'Connor 1-2 Jamie Lewis
Mark Webster 2-1 Stephen Bunting
Kim Huybrechts 2-1 Benito van de Pas
Michael Smith 2-1 Gerwyn Price
Peter Wright 1-2 Dave Chisnall
Michael van Gerwen 2-1 Keegan Brown
Adrian Lewis 2-0 Raymond van Barneveld
Jelle Klaasen 2-1 Brendan Dolan
First Round - Best of three sets
* All Sets are the best of five legs. There will be no tie-break in any set.
* All legs must begin and end with a double, meaning that a player must hit a double before he can begin scoring in each leg.
William O'Connor v Jamie Lewis
1-0 - O'Connor makes a superb start, landing a 180 in a 13-dart opening leg to break throw.
1-1 - Lewis takes out 48 on double 16 to level.
1-2 - The Welshman lands a 180 and has enough cushion to recover from initial missed doubles by posting double three to edge ahead.
1-3 - Lewis wraps up the set on double 18 to move halfway to victory.
1-0 - Lewis' miss at double 16 allows O'Connor in on double six to delight the home crowd.
1-1 - O'Connor fires in a 180 in reply to a 174 score from Lewis, who takes out double 16 to level the set.
2-1 - O'Connor posts a 177 score in being first to a double before missing three darts at tops, but Lewis misses tops himself to complete a 120 finish to allow the Limerick ace back in on double ten.
3-1 - Lewis misses tops to take out 120 for a second successive leg, and O'Connor finishes double 12 to take the set and level.
0-1 - Double five moves Lewis in front in the deciding set.
1-1 - O'Connor lands a 170 to leave tops as he hits back.
1-2 - Lewis fires in a 180 and double three to move a leg away from the win.
2-2 - Lewis misses two match darts at tops, and O'Connor finishes 71 with two darts to send the game into a sudden-death deciding leg.
2-3 - Lewis is off-target with a further two match darts, but the local favourite is unable to land two darts at double ten to take out 80, and the Welsh youngster steps up to hit double five to finally claim the victory.
Mark Webster v Stephen Bunting
0-1 - Bunting takes the opening leg to make an ideal start.
1-1 - Webster firest in the game's first 180 before landing double ten to level.
2-1 - Bunting kicks off the leg with scores of 160 and 180 to set up a possible nine-darter - but after missing out on a perfect leg sees Webster finish double ten again to break throw.
3-1 - Double top sees Webster secure the set.
1-0 - The left-hander punishes missed doubles from Bunting to claim the opener on double 16.
1-1 - Bunting opens with a 160 score for the second time in the game, and recovers from further missed doubles to land double 16 and level.
2-1 - Webster edges back ahead on double six.
2-2 - Double 16 sees Bunting level the set.
2-3 - Bunting finishes 68 to take the set and square the tie.
1-0 - Webster finishes 70 on tops to take the final set's opener.
2-0 - Webster kicks off with a 157 score and then takes out 104 to move a leg away from the win.
3-0 - Bunting's missed doubles prove costly as Webster finishes tops to secure his second round spot.
Kim Huybrechts v Benito van de Pas
0-1 - Debutant van de Pas settles any early nerves by taking the opening leg against the throw.
1-1 - Huybrechts lands a 180 before finishing double ten to level.
2-1 - Double two moves the Belgian ahead.
2-2 - van de Pas posts double four to send the set into a decider.
2-3 - The pair trade 180s before Huybrechts misses three darts at double 16 and eight, with van de Pas taking out 100 on tops - despite a bounce-out with his first dart - to snatch the set.
1-0 - van de Pas takes the second set's opener to maintain his momentum, finishing 60 on tops.
1-1 - Double 16 sees Huybrechts reply to level.
2-1 - The Belgian moves ahead with an 84 checkout.
3-1 - A third successive leg sees Huybrechts level the game as he finishes 109 for a superb 12-darter.
1-0 - Huybrechts continues his charge by finishing 76 on double four.
2-0 - van de Pas misses tops for a 114 finish, and Huybrechts capitalises with a superb 117 checkout.
3-0 - Huybrechts fires in his third 180, but misses seven match darts before punishing misses from the Dutchman in two visits by finally posting double two - to claim his first World Grand Prix win.
Michael Smith v Gerwyn Price
0-1 - Price kicks off his partypoker.com World Grand Prix debut with a 160 score before finishing 90 on double 15 to win the opener.
1-1 - Price lands a 174 score to leave 124, but a miss on double 11 allows Smith to take out 91 to level.
1-2 - Smith posts a 180, but Price holds his nerve with a 64 finish on tops to move back ahead.
1-3 - Double nine gives Price the opening set as he aims to claim a maiden World Grand Prix win.
0-1 - Price takes a third straight leg as he moves ahead in set two.
1-1 - Smith levels by taking out 52 on tops.
2-1 - Smith kicks off with a 180 before claiming a huge leg with an 88 finish.
3-1 - Smith wins the deciding set with a 76 checkout, pulling clear as Price needs nine darts to hit his starting double.
0-1 - Price once again claim's the set's opening leg.
0-2 - The Welshman lands a 180 before finishing tops to move a leg away from the win.
1-2 - Smith fires in a 180 and takes out 100 to keep his hopes alive.
2-2 - Price kicks off with a 160 score, but misses match darts at double top and ten, allowing Smith in on double ten to send the game into a sudden-death leg.
3-2 - Price's challenge ends with a nightmare leg as he misses 15 starting doubles, and Smith finishes double 14 to seal victory with a deciding leg whitewash.
Peter Wright v Dave Chisnall
1-0 - Wright takes out 16 to win the opening leg.
2-0 - The number four seed claims a scrappy second leg, punishing four misses from Chisnall by returning on double one.
2-1 - Wright fires in the game's first 180 before Chisnall finishes double 18 to hit back.
2-2 - Chisnall takes out 25 to send the set into a fifth leg.
3-2 - Wright's 146 opening score is bettered by a 160 from Chisnall, who misses two set darts at double 12 to allow the Scot in to finish tops for a 14-darter.
0-1 - Double four gives Chisnall the second set's opener.
0-2 - Chisnall moves two legs up on double five.
1-2 - Wright finishes 54 on tops to hit back.
1-3 - Chisnall takes out 93 on double seven to send the game into a deciding set.
1-0 - Both players initially miss their doubles before Wright returns on double four to claim first blood in the decider.
2-0 - Wright opens with a 146 score, with Chisnall replying with a 180 only to miss one dart at tops to punish a miss from his opponent, who returns on double ten to move a leg away from the win.
2-1 - Wright misses the bull to take out 85 for the match, and Chisnall takes out 48 on double 16 to keep the contest alive.
2-2 - Chisnall sends the match into a sudden-death leg with a superb 13-darter, opening with a 160 score and adding a 180 during the leg before finishing tops.
2-3 - Wright hits a timely 180, misses another bullseye - to take out 124 - before seeing further match darts at double eight and four go begging as Chisnall takes out 60 on tops to snatch victory from the jaws of defeat.
Michael van Gerwen v Keegan Brown
1-0 - Double ten gives van Gerwen the opening leg as he kicks off his title defence.
2-0 - van Gerwen lands a 180 and tops to move two legs up.
3-0 - Double 18 seals the opening set for the world number one with the minimum of fuss.
1-0 - van Gerwen's charge continues with double ten to claim a fourth straight leg.
1-1 - Brown lands double four to win his first leg of the game.
1-2 - The World Youth Champion breaks throw by landing double top.
1-3 - van Gerwen replies with a 180, but Brown finishes 68 on double 16 to claim the set.
1-0 - van Gerwen kicks off with a 160 score, and though Brown responds with a 180 the Dutchman finishes double 16 to move back ahead.
1-1 - The reigning champion lands his third maximum of the game, but Brown takes the leg with a sensational 152 checkout, featuring two treble 19s and double 19.
2-1 - Brown's opening doubles desert him as he misses 12 darts to start the leg, with van Gerwen posting a 180 before whitewashing his opponent on double eight for a 13-darter.
3-1 - van Gerwen's fifth 180 of the game helps him to pull clear before he takes out double ten for a 14-darter to seal victory despite a mid-game scare.
Adrian Lewis v Raymond van Barneveld
1-0 - van Barneveld misses 18 darts to start in a nightmare opening as Lewis lands a 180 and double ten for the first leg.
2-0 - The Dutchman posts a 180, but Lewis posts double top to move two legs up.
2-1 - Double eight sees van Barneveld win his first leg of the game.
3-1 - Double ten gives Lewis the first set.
1-0 - Lewis fires in a 177 and double four to move ahead.
2-0 - Lewis lands a 180 and punishes two misses from van Barneveld at double 16 by taking out 59 on tops.
3-0 - van Barneveld battles back with a maximum, but Lewis hits double three to seal his place in round two.
Jelle Klaasen v Brendan Dolan
0-1 - Dolan lands a 180 and finishes 92 for an immediate break of throw.
1-1 - Klaasen hits back with double 18 against the darts.
1-2 - Both players miss a host of doubles before Dolan lands double four to move back ahead.
1-3 - Despite a 180 from Klaasen, Dolan takes out 80 to claim the opening set.
1-0 - Dolan hits a 177 to leave 24, but Klaasen checks out 100 to move in front.
2-0 - Double 18 sees the Dutchman move two legs up.
2-1 - Dolan punishes a slow start from hi opponent by taking the leg to keep the set alive on double one.
3-1 - Klaasen opens with a 156 score and takes out 108 for the set.
1-0 - Dolan misses three darts to punish missed doubles from Klaasen, who returns on double two to edge in front.
1-1 - Dolan finishes 125 on tops to level the set - making the tie a best-of-three leg contest.
2-1 - Klaasen finishes 24 to move a leg away from the game.
3-1 - Double 18 sees the Dutchman complete victory and move into the last 16.