Vilimoni Botitu and Aminiasi Tuimaba scored two tries each while Jerry Tuwai, Asaeli Tuivuaka and Livai Ikanikoda scored a try each.
Fiji led 19-7 at half-time.
Captain, Meli Derenalagi was yellow carded in the first half for challenging a player in mid-air.
South Africa beat New Zealand 17-0 in the second Cup semifinal.
NZ beat France 29-14 in their quarterfinal while South Africa beat USA 12-10.