The world number one was denied by Michael van Gerwen in the Queensland Darts Masters final a fortnight ago, but he made amends to sign off in style in New Zealand.
Clayton was bidding to make it back-to-back World Series crowns following his win in Wollongong last weekend, and he started strongly, with an 11-dart hold in leg four sparking a sequence of three straight legs.
However, Price pinned double five to stop the rot in a crucial seventh leg, and he was indebted to the same target moments later, closing out a 12-dart break to restore parity at four apiece.
The 2021 World Champion continued his charge with legs of 15, 14 and 15 darts to move 7-4 ahead, and after Clayton fluffed his lines on the outer ring, Price converted a clinical 92 kill on double 12 to complete the comeback.
"It feels fantastic," said Price, celebrating his 26th PDC title and his second World Series of Darts triumph.
"Fair play to Jonny. I think he upped his game in the final, but thankfully I improved after the break and showed why I'm world number one.
"I think I was quite fortunate to win the last leg before the break, and I knew if I upped my scoring game I would have a chance.
"The crowd were absolutely awesome. They supported both of us tonight and they were magnificent. Thank you New Zealand!"