Scottish ace Thornton stunned world number one Michael van Gerwen with a thrilling performance as he claimed the title 12 months ago with a narrow 5-4 win in the final.
The world number seven will open up his challenge to retain the £100,000 title against Stephen Bunting when the 32-player event commences on Sunday, live on Sky Sports.
Having also hit a nine-dart finish two years ago, an achievement made more memorable with the need to both begin and end every leg with a double, Thornton has fond memories of the Citywest Hotel as he prepares to face Bunting.
"It meant everything to me to win last year and it is really good tournament for me because my big strength is double top," he added.
"My form hasn't been the best since winning it but I'm sure it will come back in Dublin because I feel so comfortable there.
"I can give anybody a game on my day and I'm quietly confident it can all click together for me again."
Sunday's opening session also features World Champion Gary Anderson taking on Jamie Caven, world number three Adrian Lewis up against Jelle Klaasen and two-time champion James Wade meeting Terry Jenkins in a repeat of the 2007 final.
Two other former finalists, Mervyn King and Raymond van Barneveld, face off, while Gerwyn Price faces Benito van de Pas, Ian White plays Kim Huybrechts and Australia's Kyle Anderson takes on fellow debutant Cristo Reyes.
Monday sees the first round conclude with the remaining eight matches, including 11-time World Grand Prix winner Phil Taylor meeting Dublin debutant Steve West.
Taylor won last week's Champions League of Darts event in Cardiff, and said: "I'm really looking forward to this, my confidence is high after last week and I've had a good preparation."
World number one van Gerwen, the pre-tournament favourite with sponsors Unibet, begins his bid to win a third World Grand Prix title against Steve Beaton in another big clash on Monday.
"I don't like not having this title and I want it back," said the Dutchman. "It is a very special one for me because it was the first one I ever won in the PDC.
"Robert Thornton got the better of me in the final last year but I have waited to put that right. I'm in great form and I am only thinking about winning. That is my only aim and I will be very disappointed with any other result."
World number five Peter Wright meets Northern Ireland's Brendan Dolan, the 2011 runner-up who is on a high coming into the event following his marriage to partner Teresa on Wednesday.
"With all the excitement in my life at present, there will maybe be less pressure on my shoulders and I can relax a little bit," said Dolan.
"I suppose darts has taken a bit of a back seat over the last month or two with the preparations for the wedding but I've given every event my best shot and I'll continue to do that.
"Peter's the number five in the world and playing well at the moment so he'll be hard to beat, but the format is short and a lot of it is about coming out of the blocks quickly and putting pressure on your opponent."
2013 finalist Dave Chisnall opens Monday's action against debutant Robbie Green, Austria's Mensur Suljovic - a semi-finalist last year - plays Northern Ireland's Daryl Gurney, Joe Cullen plays Simon Whitlock and Michael Smith faces Alan Norris.
Unibet World Grand Prix
Schedule of Play
Sunday October 2 (7pm)
First Round x8
Kyle Anderson v Cristo Reyes
Ian White v Kim Huybrechts
James Wade (6) v Terry Jenkins
Gerwyn Price v Benito van de Pas
Adrian Lewis (3) v Jelle Klaasen
Robert Thornton (7) v Stephen Bunting
Gary Anderson (2) v Jamie Caven
Mervyn King v Raymond van Barneveld
Monday October 3 (7pm)
First Round x8
Dave Chisnall v Robbie Green
Mick McGowan v James Wilson
Mensur Suljovic v Daryl Gurney
Michael Smith (8) v Alan Norris
Joe Cullen v Simon Whitlock
Phil Taylor (4) v Steve West
Michael van Gerwen (1) v Steve Beaton
Peter Wright (5) v Brendan Dolan
11/10 Michael van Gerwen
4/1 Phil Taylor
6/1 Gary Anderson
20/1 James Wade
22/1 Adrian Lewis
25/1 Dave Chisnall, Peter Wright
28/1 Mensur Suljovic
40/1 Raymond van Barneveld
50/1 Kim Huybrechts, Michael Smith
66/1 Jelle Klaasen
80/1 Stephen Bunting, Robert Thornton, Ian White, Simon Whitlock
100/1 Joe Cullen, Daryl Gurney, James Wilson, Benito van de Pas
150/1 Kyle Anderson, Mervyn King, Alan Norris
200/1 Jamie Caven, Brendan Dolan, Robbie Green, Terry Jenkins, Gerwyn Price
300/1 Steve Beaton
400/1 Cristo Reyes, Steve West
750/1 Mick McGowan
First Round: Best of three Sets. Best of five Legs per Set. All Legs must begin and end with a double.
First Round Match Odds
13/25 Kyle Anderson v 6/4 Cristo Reyes
Evs Ian White v 4/5 Kim Huybrechts
3/10 James Wade v 5/2 Terry Jenkins
6/5 Gerwyn Price v 4/6 Benito van de Pas
13/25 Adrian Lewis v 6/4 Jelle Klaasen
9/10 Robert Thornton v 9/10 Stephen Bunting
1/5 Gary Anderson v 18/5 Jamie Caven
7/5 Mervyn King v 5/9 Raymond van Barneveld
2/5 Dave Chisnall v 2/1 Robbie Green
8/5 Mick McGowan v 1/2 James Wilson
1/2 Mensur Suljovic v 8/5 Daryl Gurney
3/5 Michael Smith v 13/10 Alan Norris
9/10 Joe Cullen v 9/10 Simon Whitlock
2/19 Phil Taylor v 11/2 Steve West
1/9 Michael van Gerwen v 11/2 Steve Beaton
3/10 Peter Wright v 51/20 Brendan Dolan
Odds courtesy www.unibet.co.uk and correct at time of writing. Subject to fluctuation.