Taylor, unbeaten at the Winter Gardens since 2007, kicked off his challenge in the £450,000 event in ideal fashion by seeing off the Scottish qualifier with a comfortable victory.
Taylor kicked off three of the opening four legs with 180s as he established a 3-1 lead, and extended the gap to five legs before Henderson hit back to trail 6-2.
Taylor hit a fourth maximum as he regained his five-leg lead and then clinically took out 109 and 64 to move 9-2 up and landed another 180 before sealing victory with two double eights to finish 32.
"It was a good win and I did what I set out to do," said Taylor. "John's a better player than he showed tonight but you've got to attack your opponent and put them under pressure.
"I knew John was a little bit under pressure from the beginning so I tried to speed him up a bit and push him.
"This is my favourite venue and I love the tournament, and I feel comfortable here so it's great to still be in the hunt."
Taylor's second round opponent will be Stoke rival Andy Hamilton, who caused an upset by knocking out five-time World Champion Raymond van Barneveld with a fine 10-7 victory.
Hamilton had claimed the final ProTour qualifying place in the tournament and was the 750/1 outsider to claim the title with sponsors BetVictor ahead of the event - but has seen those odds slashed to 125/1 following the win.
Checkouts of 96 and 158 in the first two legs gave him an ideal start, and though van Barneveld hit back to 3-2, Hamilton took the next five legs without reply - landing a 13-darter and three 180s in the process - as he moved 8-2 up.
Van Barneveld won the next three to spark a revival, and after Hamilton landed a 180 and a 91 finish to move 9-5 up, he took out 48 and 96 to cut the gap to two legs.
Hamilton, though, proved too strong in the next and landed double nine to complete a win which could kick-start his year, after dropping to 20th on the PDC Order of Merit.
"It was always going to be a tough game but I knuckled down, and this event and this venue seems to bring the best out of me," said Hamilton.
"I love this tournament, I love Blackpool and I love this crowd and it brought back some great memories for me getting back on that stage. The 96 and the 158 got me going and I controlled the game from there.
"The last six months have been a horrible time for me but there's more to come and if I play well I can give Phil a good game on Wednesday. Hopefully I can progress from what I've done tonight and be more consistent, but my game's getting there."
Earlier, Premier League semi-finalist Dave Chisnall edged out Jamie Caven 13-11 in a tie-break as the pair slugged out a 24-leg thriller.
Although Caven held a slender 2-1 lead early on, following a break of throw in leg three, Chisnall hit back to take a 6-4 advantage with the aid of a 13-darter and a 14-dart finish.
Caven took the next two to level at six-all, with the next six legs all going with the throw to send the game into a tie-break at 9-9, leaving a player needing to win by two clear legs.
The pair traded tops finishes and then shared the next two legs to remain locked at 11-all as Chisnall twice missed a single match dart, with double nine then seeing the number seven seed move 12-11 up and to the brink of victory.
With Caven throwing to force a sudden-death 25th leg, Chisnall kicked off with 140, 180 - his 13th of the game - and 135 to leave 46, and eventually sealed victory at the eighth attempt.
"It was a funny game but a good game before me because I won," said Chisnall. "Hats off to Jamie because he played well and kept plodding on and hitting his doubles and pulling it back, but thankfully I broke his throw in the last leg.
"I had a feeling that the game was going to go all the way because he's a great player. Sometimes I was in control but I was probably under pressure more than Jamie because I was almost always in the lead.
"My scoring's never a problem but sometimes it's my doubles which are a bit dodgy, but luckily I won tonight and that's all that matters."
Chisnall now faces World Youth Champion Keegan Brown, who enhanced his growing reputation as a contender at darts' highest level with another composed performance, as he followed up his giant-killings at the Grand Slam of Darts and World Championship by claiming another big-name victim.
Thornton had gone into the event on a high following last weekend's European Tour triumph in Dusseldorf, but never recovered from seeing Brown take an early 5-1 lead as he suffered a sixth straight first round exit in Blackpool.
After Brown opened the game with a 14-darter, Thornton replied with a 12-darter only to see the Isle of Wight youngster win the next four to pull clear.
Thornton replied with finishes of 70, 40 and 62 as he reduced the gap to 5-4, but was crucially denied a chance to level as Brown fired in a 180 in a 14-darter to regain breathing space.
A 102 finish put him 7-4 up and he also took out another 14-darter to lead 8-5 before landing the bullseye to move to the brink of victory at 9-6.
Battling Thornton landed a 180 and finished 78 on tops to stay in the hunt, but Brown clinically sealed victory with another bull checkout, this time taking out 87 to seal his second round spot.
"I'm over the moon," said Brown. "I came here 12 years ago and watched Phil Taylor and Wayne Mardle in the final and thought it would be brilliant to play on that stage on day, and I've done that now.
"Robert's a player with Premier League experience so I wanted to get into him quickly and to take the first session 4-1 meant I could relax. Robert showed his class when he came back at me but thankfully I got there at the end.
"This is the hardest tournament to qualify for every year so I wanted to relax and play like I can do. To be in the last 16 makes me so happy."
The second round kicks off on Tuesday, with world number one Michael van Gerwen up against Welsh ace Jamie Lewis in their last 16 clash.
2013 World Matchplay finalist Adrian Lewis is up against another emerging Welsh star in Gerwyn Price, while Peter Wright takes on Andrew Gilding and Simon Whitlock faces Ian White.
BetVictor World Matchplay
Monday July 20
Robert Thornton 7-10 Keegan Brown
Dave Chisnall 13-11 Jamie Caven
Phil Taylor 10-2 John Henderson
Raymond van Barneveld 7-10 Andy Hamilton
Tuesday July 21 (7pm-11.30pm)
Peter Wright v Andrew Gilding
Simon Whitlock v Ian White
Michael van Gerwen v Jamie Lewis
Adrian Lewis v Gerwyn Price
Wednesday July 22 (7pm-11.30pm)
Dave Chisnall v Keegan Brown
James Wade v Brendan Dolan
Phil Taylor v Andy Hamilton
Gary Anderson v Mensur Suljovic
Second Round - Best of 25 legs
* Each game must be won by two clear legs, with up to a maximum of five additional legs being played before the sixth "extra" leg is sudden-death. There will be no re-throw for the bull in this instance. For example, should a Second Round game (best of 25 legs) reach 15-15, then the 31st leg would be the final and deciding leg.
Robert Thornton v Keegan Brown
0-1 - Thornton lands a 180, but Brown replies with a 168 score to leave 16 before finishing double four for a 14-darter.
1-1 - The pair trade 180s before Thornton finishes 81 on the bull to level with a 12-darter.
1-2 - Brown finishes 32 as he edges back ahead.
1-3 - Brown fires in a 180 before finishing 41 on double 16 to break throw and move two legs up.
1-4 - Brown lands tops to take his third successive leg, maintaining an average of 103.
1-5 - Thornton wires the bull to finish 86 and also misses double four with two darts to allow Brown a let-off as he returns from two earlier missed doubles to finish double ten.
2-5 - Thornton claims his first leg in five by finishing 70 on double ten.
3-5 - Brown is punished for being unable to land double 18 as Thornton steps in on tops.
4-5 - Thornton claims a third successive leg with a break of throw, finishing 62 on double 14.
4-6 - Brown kicks off with 140 and 180 before claiming a key leg with double tops for a 14-darter.
4-7 - Thornton lands a 180 but Brown holds throw to move three legs up with a 102 finish.
5-7 - Brown lands a 180, but misses tops to allow Thornton back in on double two.
5-8 - Brown kicks off with a 174 score as he regains his cushion with an 87 checkout for a 14-darter.
6-8 - Double five sees Thornton hit back.
6-9 - Brown moves a leg away from a debut victory by taking out 85 on the bull.
7-9 - Thornton lands a fourth 180 before finishing 78 on tops.
7-10 - Brown seals victory by taking out 87 on the bullseye, condemning Thornton to a sixth first round exit in Blackpool.
Dave Chisnall v Jamie Caven
1-0 - Caven misses two darts at double 14 to steal the opening leg, allowing Chisnall back on double nine.
1-1 - Caven levels by hitting double nine.
1-2 - The pair trade 180s before Caven punishes missed doubles from Chisnall with a break of throw.
2-2 - Chisnall lands a 180 before finishing double 16 for a 13-darter to break back.
3-2 - Chisnall fires in his third maximum in as many legs, before again hitting double 16 as he moves back in front.
3-3 - Tops sees Caven level.
4-3 - Caven is unable to take out 100, allowing Chisnall back in to take out 80 on tops.
4-4 - Chisnall lands another maximum, but he misses three darts at double 18 and nine to break throw as Caven capitalises on double six.
5-4 - Chisnall fires in his sixth 180 before double 16 moves him back into the lead.
6-4 - A seventh 180 of the game pushes Chisnall ahead, and he finishes 60 on tops to break throw and take a two-leg lead with a 14-darter.
6-5 - Chisnall misses one dart at double 16, and Caven finishes double two to break.
6-6 - Chisnall fires in yet another maximum, but Caven levels the game with double top.
7-6 - Chisnall regains the lead by holding throw.
7-7 - Chisnall lands a ninth 180, but is again punished for a trio of misses at double 18 and nine as Caven lands tops to avert a break and square the contest.
8-7 - A tenth 180 of the game moves Chisnall clear, before double eight edges him back ahead.
8-8 - Caven lands a maximum in reply - only his second of the game - before finishing 55 on double ten to level.
9-8 - Caven misses tops for a break of throw, and Chisnall lands a third-dart double five to move a leg away from victory.
9-9 - Caven posts his third 180, with Chisnall missing one match dart as he is unable to hit double ten for a 140 finish, allowing the Derby ace to finish double two and force a tie-break.
10-9 - Chisnall regains the lead, landing his 11th 180 of the game before hitting tops.
10-10 - Chisnall lands another 180, his 12th, to leave 64 but sees another match dart go begging as he is unable to land double 16, allowing Caven to finish 60 on tops.
11-10 - Caven lands a 177, but Chisnall finishes tops to edge back ahead once more.
11-11 - Double eight sees Caven level once more.
12-11 - Chisnall once again misses double 18 and nine, but is given a let-off to return on double nine.
13-11 - Chisnall produces the killer blow, scoring 140, 180 and 135 to leave 46, and though he initially misses four further match darts, Caven is unable to land the bull to force a deciding leg, and the St Helens man finally lands double eight to claim a thrilling win.
Phil Taylor v John Henderson
1-0 - Taylor kicks off the game with a 180 before finishing double eight to take the opening leg.
2-0 - The reigning champion opens with another maximum before landing double two to break throw.
2-1 - Henderson lands his first maximum before capitalising on two missed doubles from Taylor to land double ten to get off the mark.
3-1 - For a third time in the game, Taylor opens a leg with a 180 before he posts double eight to move two legs clear.
4-1 - Taylor endures some further double trouble before moving three legs clear on double ten.
5-1 - Taylor lands double 16 to win his third successive leg.
6-1 - Taylor clinically finishes 62 on double 16 to move five legs clear of the Scot.
6-2 - Henderson lands his second 180 before posting double 13 to hit back with his first leg in five.
7-2 - Taylor fires in his fourth maximum before taking out a third-dart double ten to regain his five-leg lead.
8-2 - Taylor finishes 109 on double 16 to move two legs away from the win.
9-2 - Taylor moves to the brink of a second round place by finishing 64 in two darts on double eight.
10-2 - Taylor lands his fifth 180 of the game before punishing a miss at tops from Henderson by sealing victory with two double eights.
Raymond van Barneveld v Andy Hamilton
0-1 - van Barneveld kicks off the game with a 180, but Hamilton claims an immediate break of throw by finishing 96 on double nine.
0-2 - Hamilton doubles his lead with a superb 158 checkout.
1-2 - Hamilton misses his chance to capitalise on two misses from van Barneveld, who returns to claim his first leg of the contest.
1-3 - Hamilton takes out 68 o double four to regain his advantage.
2-3 - van Barneveld hits back by finishing 74 on double 12.
2-4 - Hamilton takes out double 18 for a 13-dart finish.
2-5 - Hamilton fires in his first 180 before breaking throw with double 16.
2-6 - Another maximum pulls Hamilton ahead before he finishes double 16 again to claim a third successive leg.
2-7 - van Barneveld misses his chance to respond, and Hamilton returns on double ten to claim another leg.
2-8 - Hamilton lands his third 180, and though he misses tops, a miss at double eight from van Barneveld allows him back in to claim a fifth straight leg and close in on victory.
3-8 - Hamilton misses double 15 for a 150 checkout, and van Barneveld steps in to post double five to respond with his first leg in six.
4-8 - Both players land 180s before van Barneveld returns from a miss at double 18 to punish Hamilton for a treble of missed doubles.
5-8 - Double nine sees van Barneveld claim his third successive leg to halve the deficit.
5-9 - Hamilton finds another gear to land his fifth 180 before taking out 91 for a 12-darter to halt hit rival's comeback and move to the brink of victory.
6-9 - Hamilton initially misses double 14 for a spectacular 148 checkout, and is then unable to finish double 14 and seven as van Barneveld lands double 16 to keep the game alive.
7-9 - van Barneveld takes out 96 on double 18 to win his fifth leg out of six to continue his battle.
7-10 - Hamilton initially misses double nine to finish 123, but returns to hit the bed at the second time of asking to secure a memorable win.