Losana Lutu scored Fiji Bulikula's first World Cup try during their debut against New Zealand at McDonald Jones Stadium.
After Stacey Waaka opened the scoring for the Kiwi Ferns in the second minute, Fiji took control through possession, field position and physical defence.
Lutu crossed after Lorren Ieli's powerful run and quick play-the-ball created an opening for captain Sereana Naitokatoka. Five minutes later, Sienna Laing kicked through a Lutu grubber to extend Fiji's lead.
Waaka scored again shortly before half-time, but New Zealand trailed 12-4 at the break. It was the first time the Kiwi Ferns had been behind at half-time against a team other than Australia in World Cup history.
Fiji defended desperately after the interval despite injuries to Tamika Jones, Maria Paseka and Laing. Zehara Temara's penalty levelled the scores, and another penalty put New Zealand ahead after Fiji missed a chance to take the lead.
With three minutes remaining, Raecene McGregor's cross-field kick found Leianne Tufuga, whose try sealed an 18-12 comeback win.
Fiji next face the Papua New Guinea Orchids, while New Zealand host France in Christchurch next weekend.