The Fijians had to fight back from a first half deficit after Namibia flyhalf Theuns Kotze slotted three successive drop goals before Fiji seized control of the match with two tries inside two minutes.
Goneva scored his third try in the final minute of the half to give his side a comfortable 32-15 lead at the break.
Namibia abandoned their stodgy game plan and adopted a running game that lead to tries for lock Heinze Koll and fullback Chrysander Botha to give the Fijian side a fright.
But Seremaia Bai added his third penalty and Napolioni Nalaga scored a late try to blow the scoreline out.