Inside-center Giteau, playing in his 50th Test, scored two tries and kicked three penalties and four conversions in Montpellier, France. Drew Mitchell touched down three times as the Wallabies ran in seven tries to Fiji's two.

Two-time champion Australia moved to a maximum 15 points through three games to ensure top spot in Group B ahead of Fiji and Wales. The Wallabies will face defending champion England or Tonga in the last eight on Oct. 6 in Marseille.

"We didn't play well in the first half, but it showed that when we were under the pump we were able to perform," Giteau said after being named as the man of the match. "Now we've got to show that we can do it for 80 minutes."

The Wallabies took 17 minutes to get their first points against a second-string Fiji team at Montpellier's Stade de la Mosson. Giteau scored 17 of his team's 22 points at halftime with Mitchell's try adding the others.

Winger Isoa Neivua carried three Australian tacklers over the tryline for Fiji's only points of the half. The Fijians also got the first try after the break when Aca Ratuva broke clear.

Adam Ashley-Cooper secured the bonus-point try in the 57th minute when Giteau fed him with a quick pass. Mitchell then completed his hat-trick with touchdowns either side of a Stephen Hoiles try.

Fiji, which fell to its first loss, will face Wales on Sept. 29 in Nantes for the group's other quarterfinal spot.