A crowd of 25,065 watched Tonga shut out Lebanon 36-0 at CommBank Stadium on Friday night, keeping their record unbeaten.
The win sets up a sold-out clash with Samoa next Sunday, with a place in the final four at stake.
Tonga will also seek to avenge last year's 28-point loss to Samoa in Brisbane.
Coach Kristian Woolf had warned against overlooking Lebanon, and his side had to withstand a determined challenge before their superior class showed.
With Isaiya Katoa absent through an ankle injury, Tui Lolohea filled in at halfback as Tonga scored seven tries.
Katoa is expected back against Samoa.
Tonga's defence, which had underpinned their win over England the previous week, again proved vital during a bruising first half.
Lebanon could not breach the line, while Tonga took an early lead through Sione Katoa, who finished a Lehi Hopoate pass in the 13th minute.
Paul Alamoti added another try before Tolu Koula raced 90 metres just before halftime, extending Tonga's advantage after Jason Saab tapped back an Alex Conti kick.
Haumole Olakau'atu led the Sipi Tau and delivered a forceful performance in attack and defence.
Jojo Fifita scored twice after halftime, and Leka Halasima's try with 11 minutes remaining effectively sealed the result.