Maiden ranking title for Joyce on day two of PDC Summer Series
Newcastle's Joyce had won through to a maiden final with some fine displays on the day, enhancing his hopes of a Betfred World Matchplay debut in the process.
He had looked set to settle for the £6,000 runner-up cheque after Chisnall opened up leads of 6-2 and 7-3, only to survive five missed match darts as he finished the stronger to take the £10,000 title.
Joyce is now in the provisional qualifying places for the World Matchplay, with the 32-player field set to be confirmed on Sunday evening following the five days of the PDC Summer Series.
He has also joined the elite group of players to taste glory on the PDC ProTour this year, including Wednesday's Day One winner Michael van Gerwen.
"It's unbelievable - it hasn't sunk in yet," admitted Joyce afterwards. "It's a fantastic win.
"At 7-3 down in the final I thought the game was gone. I was trying to enjoy the rest of the match and make the score more respectable, but Dave tightened up a bit, he missed his chances and I punished him.
"To win an event like this, you need a couple of rounds where you get the rub of the green and I got that today. I don't want to be a one-hit wonder and I've got to build on this."
Joyce could now be set to return to the Marshall Arena from July 18-26 to compete in the World Matchplay, should he hold on to his qualifying place in the 16 ProTour Order of Merit positions.
"I haven't been thinking about the World Matchplay," he admitted. "I've got to take it one game at a time over the next three days and see how I play, so I'll go into Friday with the same mentality."
Joyce also revealed that some words of encouragement from South African star Devon Petersen had inspired him going into Thursday's event.
"I'm not the most consistent player but I know I've got it in me," he said. "I got beaten in the first round on Wednesday and it was a poor game, I didn't play well.
"I was talking to Devon Petersen this morning and I said I've lost a bit of confidence in my throw. He showed me a practice game and had a few words of encouragement, and I felt a different player."
He averaged over 100 in wins over Andy Hamilton and Chris Dobey as well as defeating World Youth Champion Luke Humphries and Latvia's Madars Razma.
Joyce then saw off Unibet Premier League leader Glen Durrant 6-5 in the quarter-finals, and averaged 102 in a 7-3 semi-final win over Gary Anderson.
Chisnall had held the upper hand in the early stages of the final, pulling clear to lead by four legs on two occasions as he moved to the brink of victory.
Joyce won the next three before four missed doubles from Chisnall in leg 14 allowed him to level the tie, and when his rival missed the bull in a high-quality deciding leg he stepped in on double 16 for glory.
Chisnall had been agonisingly close to a 15th PDC ranking title and a first triumph in 12 months as he won through to the final.
Following early wins over Aaron Beeney and Jamie Lewis, Chisnall defeated the Dutch trio of Benito van de Pas, Maik Kuivenhoven and Martijn Kleermaker to reach the semi-finals.
There, he was a 7-5 winner over Nathan Aspinall before his five missed match darts proved costly in the final against Joyce.
Aspinall was denied by Chisnall in his bid to win a third Players Championship of the year, having defeated World Champion Peter Wright and James Wade in his run to the semi-finals.
Anderson was aiming to win his second Players Championship of 2020, with his five wins on the day including a 110 average in a whitewash of Ryan Murray.
Kleermaker enjoyed his best finish since joining the PDC circuit in January as he reached the quarter-finals alongside Durrant, Wright and Clayton.
Wednesday's Day One winner Van Gerwen was defeated by Kuivenhoven in a deciding leg at the last 32 stage, with Gerwyn Price also losing out in round three despite an earlier 116 average against Steve Lennon.
The PDC Summer Series continues on Friday with Day Three in Milton Keynes, with a further £75,000 in prize money on offer.