Australia claimed a Pacific Cup double with their men and women both winning the tournament.
The Kangaroos held off Tonga, who upset title holders New Zealand to reach the men's final, to secure a 20-14 victory while Australia's women beat New Zealand 24-14.
Manly Sea Eagles fullback Tom Trbojevic grabbed two tries as the Kangaroos won the Pacific Cup for the first time.
Tonga, backed by a sea of fans in red at Sydney's Parramatta Stadium, took a shock early lead when Sione Katoa crossed.
But Australia asserted themselves and went 20-4 ahead before their opponents fought back.
Haumole Olakau'atu reduced the deficit after getting on the end of a Tuimoala Lolohea grubber kick and then Eliesa Katoa put them within six points - but the hosts held on.
Victory for Australia's women avenged a 12-6 loss to the Kiwi Ferns in last year's final. The Jillaroos' tries were scored by Julia Robinson, Isabelle Kelly, Tiana Penitani, Tamika Upton and Tarryn Aiken.
Elsewhere, New Zealand beat Papua New Guinea 54-12 in a play-off to remain in the men's top tier, while Samoa's women thumped Papua New Guinea 34-12 to earn promotion to the top flight.