The result means that Fiji are promoted to the Oceania Cup next year, alongside New Zealand and Tonga, as Australia sits out in 2020 due to their tour of England.
Fiji were coming off a brilliant 44-18 win over Samoa last week, and had been bolstered by the return of Maiko Sivo, the Eels winger who topped the NRL try scoring charts this year.
Papua New Guinea hadn't played since a mid-year defeat to Samoa, though participating in the recent Nines World Cup, and a camp in Port Moresby, meant they weren't coming in completely cold.
The Kumuls had also been bolstered by the inclusion of former Kangaroos representative Alex Johnston, though were without James Segeyaro (fighting a provisional ASADA ban) and Kurt Baptiste (injury).
Fiji started well, reflecting the confidence gained from the Samoan performance. They dominated the first quarter, before prop Kamikamica bundled his way over in the 22nd minute.
But unlike last week, they couldn't go on with it and lacked the necessary patience in their play.
Fiji scored three tries in the first 45 minutes, but mistakes on the following set each time opened the door for PNG to reply almost immediately.
The pick of the Kumul's tries went to Edene Gebbie, as the winger sprinted 50 metres up the middle to score, before a dazzling sidestep to beat the fullback.
PNG got better as the match progressed, and successfully negated the influence of Fiji playmaker Brandon Wakeham, especially with their kick pressure.
They looked the more likely winners in the final 10 minutes, and only some desperate Fijian defending, and a couple of contentious calls from referee Chris Kendall, who seemed to struggle with the pace of the game, stopped them from gaining the decisive try.
Fiji 22 (T. Kamikamica, B. Wiliame, V. Kikau, B. Nakubuwai tries; B. Wakeham 3 goals)
Papua New Guinea 20 (R. Martin, W. Boas, E. Gebbie tries; Martin 4 goals).
Halftime: 12-14
