Australia captain George Gregan revealed his relief as the world champions beat Ireland to top Pool A.
Gregan believes Australia must improve
The Wallabies now face Scotland after winning 17-16 in Melbourne, while the Irish face a tougher quarter-final obstacle in France.
And Gregan said: "We're happy to have got through that.
"Obviously we didn't play the way we wanted to but that was a lot to do with the way the Irish performed."
Australia had initially looked on course to dominate the match as George Smith scored early on.
And the trusted boot of Elton Flatley moved them 14-6 ahead shortly after the re-start.
But Ireland produced a thrilling fightback as Brian O'Driscoll slid into the corner to score.
Flatley added another penalty, before O'Driscoll's 67th-minute drop goal set up a tense finale, which the Australians just edged.
Gregan said: "They put us under a lot of pressure and had most of the field position in the whole game."
And looking ahead to next weekend's tie against Scotland, he added: "There's lots of areas to improve but we hung in their and won a tight match which is always a good thing to do."