Rising star Viliami Iongi grabbed two tries for Tonga, who were captained by Worcester's Lutui, to underline his World Cup credentials but it was not enough to propel his side to victory and they must now overturn a 15-point deficit in the return clash next weekend.
Fiji pounced on an error from the visitors to set up the opening the score for Goneva in the third minute but Tonga soon hit back with a well-worked try of their own through fullback Viliami Iongi. Back came Fiji with Vitori Buatava setting up Nasiga for their second try that was converted by Bai.
The hosts extended their advantage before the break when Murimurivalu carved his way through the Tongan defence to notch a try that was again converted by Bai to give Fiji a 21-5 lead at the break.
Tonga rallied at the start of the second half with rising star Iongi grabbing his second try just a minute after the restart. Samisoni Fisilau landed the sideline conversion to raise hopes of a comeback but despite maintaining their efforts, two penalties from Bai snuffed out their challenge.