The teams will next meet at the Rugby World Cup in Japan in October 2019.
"This is the level we need to play every game and we managed to do it in today's game," Fiji captain Akapusi Qera said.
"We know we will get Georgia again in 2019 and that will be a different game. But it's a boost for us as a new team and for some of the new players."
Radradra was a strong runner in midfield and had a hand in the second try scored by Seniloli.
Wingers Nemani Nadoli and Vereniki Goneva were also powerful with the ball in hand and lock Leone Nakarawa enlivened the match with his offloading skills.
Earlier, Tonga built a 28-6 lead then held on with 13 men to beat Samoa 28-18 in a match between the first-round losers.
Tries to wingers Viliami Lolohea and Cooper Vuna gave Tonga a 17-6 lead at halftime and they reinforced that advantage with a second-half try to Nili Latu.
Halfback Sonatane Takulua kicked two conversions and three penalties for 13 points.
Tonga will face Fiji in Lautoka next weekend while Samoa moves on in two weeks to Rugby World Cup qualifying matches on the back of successive losses in the Pacific Nations Cup.
"We didn't get the outcome we wanted in terms of wins but I think we can take huge positives out of this," Samoa captain Chris Vui said.
"We've shown that we can play rugby but it's just those silly errors that cost us."Tonga took an early 7-0 lead Saturday with a try to Lolohea. Samoa closed to 7-6 with two penalties before Vuna dived over from a tapped penalty.
Takulua kicked three penalties to make the lead 23-6 and Latu took the game beyond Tonga's reach with a try in the 51st minute.
Tonga's discipline crumbled in the last quarter — it conceded 14 penalties in the match and two yellow cards in the last 10 minutes to finish with 13 men.
Samoa took advantage with late tries to replacements Ed Fidow and Melani Matavao.
