Winger Adam Ashley-Cooper scored three tries in seven minutes in the second half for the Wallabies, who had been heavily criticized for their 15-6 loss to Ireland last week, but showed on Friday how dangerous they can be when allowed to control the pace of the game.

Australia ran in 11 tries — several from more than 50 meters out — at Wellington Regional Stadium but Deans faces injury concerns with center Anthony Faingaa knocked unconscious in the final minute of the Pool C encounter, while fellow midfield backs Rob Horne has a fractured cheek bone and Pat McCabe dislocated his shoulder.

Fullback Kurtley Beale also "tightened up" and was replaced shortly before halftime, while number eight Wycliff Palu also had to come off with a hamstring complaint.

"It's pretty extensive, the full extent we don't know," Deans told reporters after the match that ended with replacement number eight Radike Samo playing on the wing.

"We may have (to call people into the squad), we will have to see what the medics say. We have an eight day turnaround and ... we will wait until we have learned the full extent of it before we make any decisions." The injuries on Friday add to the concerns over Digby Ioane (thumb) and David Pocock (back), who were not considered for the US match while James O'Connor (hamstring) and captain James Horwill (shoulder) were given time off to try to recover.

Australia now play Russia in Nelson on Oct. 1 and are likely to finish second in the pool and could meet South Africa in the quarterfinals and then New Zealand in the semifinals should both sides make the final four.

Friday's match may have pleased Deans with the result and some of the support plays and width they achieved, but he will remind the Wallabies they will not get as much quick ball or space against better sides in the knockout phase.

The Tri-Nations champions had a nervous opening five minutes but then scored two electric tries to inside center Rob Horne and flanker Rocky Elsom after they recycled the ball at lightning pace.

The US then had the better of the next 20 minutes after captain Tim Usasz had broken out from inside his own half that gave them some much needed momentum.

Despite holding out for several minutes, the Wallabies finally broke when US number eight JJ Gagiano exploited a poorly defended blindside from an attacking scrum to bring the crowd to the feet as he scored the first try against Australia at the tournament so far.

The Wallabies, despite being forced back on their line again, highlighted how dangerous they were with ball in hand as they swept 90 meters down field for fullback Beale to finish off, which Cooper converted.

Faingaa secured the bonus point less than five minutes later to give the Wallabies a 22-5 lead at halftime.

The Wallabies continued their resurgence after the break with winger Drew Mitchell and replacement center McCabe both crossing in the first 10 minutes to ensure there was no chance of an American fightback.

Ashley-Cooper then went on his scoring burst before Faingaa scored his second after another long-range attack and Radike Samo took the final pass from Ashley-Cooper to score their final try. Berrick Barnes converted four of their second-half tries.

"I thought we had a good first half ... we ran out of steam at the end but I'm immensely proud of the guys," said Usasz.

"That's the difference when you play the best sides in the world, they really punish you for your mistakes."