Cook Islands took a 6-4 lead in their first Test against Australia before the Kangaroos recovered to win 66-6 in Townsville on Saturday night.
The victory left Australia undefeated in the World Cup pool stage and set up a semi-final against Samoa or Tonga in Sydney on November 8.
Reece Walsh and Tom Dearden strengthened their claims to keep the fullback and halfback spots, ahead of James Tedesco and Sam Walker respectively.
Walsh, despite a knock to the left ankle he had surgery on late in the season, scored and set up five tries.
Coach Kevin Walters praised his contribution but said Tedesco remained in contention.
"That's Reece, that's what he brings to the team," Walters said.
"It's a good position to be in as coach."
Dearden supplied two first-half try assists, combining effectively with Cameron Munster, who took over goal-kicking after Walsh's foot complaint.
Harry Grant started at hooker and will wear the No.9 for the rest of the tournament.
Australia led 28-6 at halftime after the Cook Islands challenged strongly early, but the Kangaroos pulled away after the break.
Jack Bostock and Tom Trbojevic each scored three tries, while Jacob Preston made two line breaks and scored.
Australia's ball handling remained a concern: its completion rate was below 70 per cent, which may not be enough in the knockout rounds.
Bench forward Cameron Murray withdrew late with a sore calf, but Walters said he and Walsh were not in doubt for next week.
Cook Islands coach Karmichael Hunt said he was proud of his side's opening 40 minutes against Australia.
Veteran Brad Takairangi played his final match for the Cook Islands after a Test career featuring 17 appearances for the nation and four for New Zealand.
He led the team's pe'e haka before kick-off, while Australian playmaker Ethan Strange made an impressive Test debut from the bench.