The Kiwis won on the back of a dominant pack and scintillating displays by fullback Keano Kini and five-eighth Dylan Brown.
Tonga needed to win by 18 points to qualify for the final in Sydney on November 9 but were never in the hunt.
Kini had only played six NRL games for Gold Coast in 2025 due to a neck injury.
His late insertion at fullback by coach Stacey Jones was a masterstroke after he'd made a late switch of Charnze Nicoll-Klokstad to centre.
The 21-year-old Kini razzled and dazzled from the outset with his electric feet too hot for Tonga to handle.
Kini started and finished an 85m raid in combination with Casey McLean.
The hosts started to dominate through the middle with Joseph Tapine, James Fisher-Harris and Moses Leota immense.
Brown, so effective when he runs the ball, pinned the ears back from close range to make it 12-0.
He finished a length of the field movement with a cross-field kick for the athletic McLean to leap high and score his seventh try from just three Tests.
Second-rower Briton Nikora was lethal on the right edge and centre Matt Timoko made it 24-2 at halftime.
On the cusp of the break, Kiwi forward Erin Clark was sin-binned.
Tonga crossed for their first try through forward Demitric Vaimauga after dynamism from bench hooker Soni Luke.
Their joy was short lived, with Brown setting up Nicoll-Klokstad for a try.
Brown made it a double to showcase his outstanding Pacific Cup form as the floodgates opened.
The Kiwis received powerhouse performances from their bench forwards Xavier Willison, Naufahu Whyte and Clark.
Tonga second-rower Eliesa Katoa was in the wars, leaving the field for two HIAs during play after suffering a head knock in the warm-up.
His side missed tackles, dropped the ball and were a major disappointment in the Pacific Cup after losing 34-6 to Samoa the previous week.
The return of lock and co-captain Jason Taumalolo from a knee injury did give Tonga more oomph up front, but the Kristian Woolf-coached side has plenty to work ahead if they are to figure at next year's World Cup.
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