Samoa had taken the lead after three minutes when Stephen Crichton – whose golden-point drop goal beat England in the 2022 semi-final – landed a penalty in front of the posts.
But Australia led soon after when Tom Dearden picked up from a scrum and blasted through the non-existent line to score.
Australia’s next two tries came after they got six again thanks to poor Samoa discipline. Jacob Preston burst under the posts on 15 minutes; 10 minutes later, Tom Trbojevic – joint-leading try scorer at this Men’s World Cup – got his eighth try of the tournament, benefiting after Crichton reached into the ruck.
Walsh got in on the party – celebrating with a backflip – and the scoring was topped before half-time when Bradman Best bounced off tackles and into the corner.
Both sides were fired up by regional rivalry, as the Siva Tau showed pre-match. Samoa’s Brian To’o leaned his forehead into the face of Tino Fa’asuamaleaui, the Australia prop who played for Samoa in 2019.
But Samoa’s passion dissolved into frustration as the game got away – not helped by some questionable refereeing decisions.
The most egregious came on the half-hour, when Crichton appeared to have grounded to close the score to 16-6 after Francis Manuleleua had beaten Walsh to a high ball.
But a slow-motion replay led to the debatable conclusion Manuleleua had knocked on. It was the final straw for some Samoa players – Spencer Leniu was sin-binned for speaking out of turn to referee Adam Gee just before the break.
Crichton did get his try in the second half after Walsh dropped a bomb, and Izack Tago scored in the corner with 18 minutes left.
But Walsh quickly responded after both Samoan scores, keeping them at arm’s length while scoring his first international hat-trick. Bostock added gloss with eight to go.
The damage was done – mostly by Samoa to themselves.