Reece Walsh set up five tries in Australia's 66-6 win over Cook Islands, earning his second man-of-the-match award at the World Cup.
He took another knock to his left ankle, which he injured playing for Brisbane on August 15.
The 24-year-old had suffered a high-grade syndesmosis injury and undergone surgery.
Walsh credited Broncos rehab staff Lindsay Self and Luke Anning with helping him recover and advising him not to fear a knock.
They said the tightrope fixation and rod made the ankle stronger than usual, Walsh said.
Walsh said coach Kevin Walters warned him in August that selection was not guaranteed, but he worked hard to return.
Walsh was widely considered slightly ahead of James Tedesco, who starred in Australia's 36-22 win over Fiji, which Walsh missed.
Walsh said Walters had not told him who would play fullback against Samoa in Sunday's Allianz Stadium semi-final: "He actually hasn't."
He said the squad would support Walters' decision and praised Tedesco's preparation as a valuable example.