Raitini touched down twice in the first half as Fiji dashed to a 17-7 halftime lead and completed his hat-trick less than a minute into the second spell, sealing his team's win.
Joji Baleviani Raqamate, Ilai Tinai and Levani Botia also scored for Fiji, who won by six tries to two. New Zealand, who won the World Series last year for the 10th time, scored a try in each half through Tim Mikkelson and Kylem O'Donnell.
Both Fiji and New Zealand dropped a match in pool play on Saturday but rallied to win their quarterfinals and semifinals, setting up Sunday's final showdown.
Hosts Australia entered the second day of the tournament as favourites after beating Fiji to finish unbeaten in pool play. But in one of the largest upsets in recent seasons, Australia were beaten 21-14 in the quarterfinals by Kenya, who qualified in second place from Pool C.
Dennis Ombachi scored Kenya's match-winning try in stoppage time.
New Zealand edged Argentina 12-7 in their quarterfinal, then ended Kenya's brave run with a 15-5 win the semifinals. Fiji beat Pacific rivals Samoa 19-7 in the quarterfinals and South Africa 21-10 in the semis.
South Africa went on to beat Kenya 41-7 in the playoff for third and fourth.
Raitini's first try gave Fiji an early lead in the final but New Zealand rallied briefly with to Mikkelson, converted by Tomasi Cama, which gave them a 7-5 lead.
Fiji then seized control of the match with a try to Botia and further tries to Raitini on either side of halftime.
In another surprise result on Sunday, unheralded Spain won the Bowl, beating England 19-14 in the final after earlier upsetting Tonga and Wales.
Source: SuperSport
