Playing in their first Cup final of the season, the Fijians overcame a yellow card and a 12 point half-time deficit, with Alosio Sovita Naduva bagging a hat-trick in a man of the match performance.
It was Fiji's first World Series win since Hong Kong ten months ago and coach Gareth Baber said the players stepped up when it mattered.
"I think everything is down to them really: their character, their belief, their love for their country and their families back home and their faith in god," he said.
"We just said at half-time we're capable of scoring from anywhere, just believe in what we do, trust it and at that stage we didn't know we were going to win the game.
But once you create a bit of momentum it sort of ebbs into other areas of the game as well. We were good in the contact area, the tackle and then we finished with lovely tries."
After topping their pool on day one, the Olympic champions left it late to beat Samoa 12-10 in the Cup quarter finals before holding on to beat hosts New Zealand 14-12 in the semi finals.
Fiji's first New Zealand title since 2010 lifted them two spots to third in the World Series standings after four rounds, 15 points behind leaders South Africa.
"It gives confidence but you keep feet firmly on the ground and you move onto the next thing and the next thing is to go back to Fiji, recover and work on some of the areas that we need to keep pushing," said Gareth Baber.
"To make sure that we're pushing out standards continuously and hopefully that corresponds with wins in tournaments like Vegas and Vancouver."
Samoa produced their best performance of the season, bouncing back from their quarter final defeat by Fiji to edge England 22-17 in extra-time and Kenya 19-15 in the playoff for fifth place.
The Manu are tied with Kenya in eighth place on the overall standings.
Meanwhile Papua New Guinea showed strong improvement from Sydney, thrashing France 35-0 0 before being outgunned 42-12 against the United States to finish a credible 11th.