Australia produced a strong second-half performance to see off Pool C rivals Italy in their Rugby World Cup opener.
It was a scrappy opening 40 minutes, with little action in either 22 as both teams struggled to cope with the rain and windy conditions.
But the Wallabies exploded into life after the break with Ben Alexander, Adam Ashley-Cooper and James O'Connor all going over.
Digby Ioane showed incredible speed to score their fourth try.
Mirco Bergamasco kicked over both penalties for the European side in the first period.
The Australian tries came in a devastating 17-minute burst which turned the match on its head.
Coach Robbie Deans had decided to make a change just six minutes into the second half, with O'Connor replacing Anthony Faingaa, and the Wallabies soon regained the lead.
Ioane's break and fine link work by Radike Samo gave them the position for prop Alexander to trundle over for a 49th-minute try that made it 11-6, with O'Connor failing to convert.
A second try soon followed as a stretched Italian defence was cut apart by Ashley-Cooper's angle of support off Cooper. The winger touched down behind the posts to hand O'Connor an easy conversion.
O'Connor was next to cross the line as an inside pass from Cooper allowed the replacement to wriggle past Carlo Antonio Del Fava for a third try, which he converted.
The bonus point was bagged as replacement Luke Burgess and Cooper combined to send Ioane racing over for another converted score.
"We did well in the second half," said Wallabies coach Robbie Deans. "We probably did well in the first half too, although it was not shown on the scoreboard.
"We took time to settle, Italy had the benefit of the breeze in the first half but our intensity at the contact area was better in the second half.
"We have a lot of respect for the Italians, they defend well and will cause sides problems."
Italy counterpart Nick Mallett paid tribute to the potency of Australia's attack in the second half.
"When they do get quick front foot ball they are a very difficult side to defend against," he said.
"We had a couple of opportunities in the second half particularly from a push-over try when the ball wasn't controlled at the back of the scrum, but all in all I'm pretty happy."
Italy will await news on Martin Castrogiovanni after the talismanic prop limped off near the end with an apparent groin injury.
Australia: Beale, Ashley-Cooper, A Faingaa, McCabe, Ioane, Cooper, Genia; Kepu, Moore, Alexander, Vickerman, Horwill, Elsom, Pocock, Samo. Replacements: O'Connor for Faingaa (48), Burgess for Genia (62), Polota-Nau for Moore (62), Slipper for Alexander (67), Higginbotham for Elsom (70), McCalman for Pocock (60). Not Used: Simmons.
Italy: Masi, Benvenuti, Canale, Garcia, Mi Bergamasco, Orquera, Semenzato; Lo Cicero, Ghiraldini, Castrogiovanni, Del Fava, Van Zyl, Zanni, Barbieri, Parisse. Replacements: McLean for Garcia (60), Bocchino for Orquera (74), Gori for Semenzato (71), Cittadini for Lo Cicero (69), Bortolami for Del Fava (60), Derbyshire for Barbieri (51). Not Used: D'Apice.
Ref: Alain Rolland (Ireland).