Matt Giteau has celebrated his 50th Test in style by bagging 27 points to pilot the Wallabies to a 55-12 Rugby World Cup pool win over Fiji.

The flattering seven-tries-to-two result seals top spot in pool B and a likely quarter-final with reigning champions England in Marseille on October 6.

Winger Drew Mitchell finished with a hat-trick as Australia crossed for three tries in the final 10 minutes after Fiji closed the score to 28-12 after half-time.

Giteau scored two of the Wallabies first three tries and set up the fourth to Adam Ashley-Cooper to show why he's the highest-paid player in Australia.

The milestone man kicked seven from nine in front of the posts at Stade de la Mosson to grab the third highest individual World Cup haul by a Wallaby.

Australia opened up a 22-0 lead after 36 minutes but failed to shut out the flamboyant Fijians who exposed some defensive deficiencies in the second-half.

In a scrappy match with plenty of niggle, Australia dominated the set-pieces but struggled to execute their own plays in attack.

But the Islanders, undoubted crowd favourites in Montpellier, failed to make them fully pay with even scrappier handling of the little ball that came their way.

The win came at a cost for the Australians with reserve back Scott Staniforth replaced with a suspected upper arm/shoulder injury after being hit late with his first touch of the ball.

It took until the 17th minute for Giteau to open the scoring with a try and that came courtesy of a fair degree of luck.

Lote Tuqiri was sent on a sideline break by Wycliff Palu before passing inside to a Fijian cover defender who tapped the ball up for the inside centre to pounce.

Fullback Chris Latham, in red-hot form, created the second Australian try in the 30th minute with a smart grubber for Mitchell to score for a 17-0 lead.

No.8 Palu was an ominous presence in attack throughout the 40 minutes and fed off for Giteau to burrow over for his second try and a 22-point lead after 36 minutes.

Australia's superior scrum reaped two early tight-heads and made life tough for the Fijian pack throughout while the Islanders also struggled to retain their own ball in the line-outs.

Rookie five-eighth Berrick Barnes slotted a 32m field goal just like last week against Wales to stretch Australia's lead to 28-5.

Brisbane product Mosese Rauluni then busted through a lineout to feed flanker Aca Ratuva for a try which almost brought the biggest roar of the match.

Two streakers gained that honour when they broke on to the field, with one knocked out and the other safely going from tryline to tryline before being arrested.

Mitchell was lucky to get his hat-trick with a fair degree of doubt over his last two length-of-the-field tries. AAP