Australia overcame a sloppy start to book a Rugby World Cup semifinal against New Zealand with a 33-16 victory over Scotland at Suncorp Stadium.

Two pieces of opportunism for second-half tries to Stirling Mortlock and George Gregan broke the quarterfinal open for the Wallabies after they were held to 9-all at halftime.

They could pay a high price for the 11th straight RWC victory, a record for consecutive wins, with young gun Matt Giteau hobbling off with a leg injury.

The Wallabies may be without the reserve utility back for next Saturday's semifinal against the All Blacks, who put South Africa to the sword 29-9 in Melbourne.

Australia will certainly need to lift their performance if they are to seriously challenge the impressive All Blacks after an indifferent display against the struggling Scots.

Handling errors, line-out losses and missed opportunities plagued the first half where goal-kickers Elton Flatley and Chris Paterson traded three-pointers

But surgery to the misfiring line-out, in the form of Matt Cockbain, on for George Smith, set a better platform and Australia made the most of their extra possession.

Smith wasn't the only key man given an early rest as playmaker Stephen Larkham, whose kicking game was again below par, was replaced by Giteau in the 53rd minute.

Skipper Gregan was also given an early shower, with Eddie Jones handing Chris Whittaker 15 minutes to impress.

With the game in the balance it was outside centre Mortlock, seen as an Australian backline messiah before the tournament, who saved the day.

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