A break of 59 helped Allen win the opening frame but a century from Trump levelled the scores at 1-1.
However, Antrim man Allen would then dominate the decider as he won six frames in a row.
Trump looked like levelling the match at 2-2 as he led 62-0 but Allen would have different ideas as he pinched the frame on the final black.
It would be a case of déjà-vu in frame five as Allen made a 75 break after Trump broke down on 48, with Allen making a century in frame six to lead 5-1.
Trump would have a chance in frame seven but missed as Allen made it 6-1 and then he won the next frame to extend that advantage.
The run of six frames in a row would come to an end in the final frame of the first session as Trump made a much needed 62 break to get over the line 7-2 behind.
Trump – who has won three ranking events already this season – would make it 7-3 by taking the first frame of the evening session with a break of 77.
A run of 57 helped Allen make it 8-3 and then he was one away from victory as breaks of 33 and 42 helped him take frame 12.
The victory was complete thereafter as Allen’s break of 75 helped him secure the winners’ cheque of £150,000.
“This is why we play the game, to play in front of the best crowds in the best events against the very best in the world,” Allen told ITV Sport.
“There’s no doubt that Judd has been far and away the best player in the planet this season.
"It’s up to the rest of us to catch up and I’m fed up texting him after every tournament to say well done.
"It’s nice to get one over him but he’ll be back and I’m sure he’ll give me a few bashings as the years go on.
"It’s been a very poor start to the season but I’ve been putting the work in and practicing really hard.
"I’ve been a bit lost as I lost someone in the summer who’s been by my side since I’ve been 12-years-old.
"Joe Shortt was a big part of my life both on and off the table and my dad and I lost one of our closest friends.”
Allen hopes the victory will help propel him to further success as he begins his defence of the UK Championship next week.
"To win any tournament like this against players who are on top form and won over the last 12 months, means your game is in good shape,” he added.
"I’ve been working so hard to get my game back and I don’t want to see other people win all the trophies, I want to be a part of that.
"Ultimately, you have to play better and I hadn’t been doing that.
"To come here and find some form is probably more important than anything else.
"It’s great to be backing winning but I’m not taking anything for granted.
"I’ll be straight back home on the practice table for the start of the UK Championship.”