Isapea were first on the board in the first half in the 25th minute when prop Bradley Yano bulldozed over to score.
Solomon Pokari had no trouble adding the extras to make it 6-0.
The Gulf boys extended the lead in the second half when winger John Horope dived over in the 51st minute.
Pokari made it two from two to put his side comfortably in front.
But the Vipers struck back just 8 minutes later through Brandan Gutono.
A successful conversion from Quintan Ragi made it 12-6.
