Skipper Stirling Mortlock should only miss one World Cup match in a major relief to the Wallabies after their 32-20 pool B win over Wales on Saturday.

Centre Mortlock suffered a partial dislocation of his shoulder in scoring the second of Australia's four tries in an entertaining battle at Millennium Stadium.

He was treated for several minutes before resuming for the final five minutes of the second half but was replaced at half-time with the Wallabies ahead 25-3.

Mortlock said it was a precautionary move and indications are he'll be rested from next Sunday's Fiji clash in Montpellier and should return against Canada in Bordeaux on September 29.

"In scoring that try I subluxed my shoulder," he said.

"It pretty much went straight back in and soon as it did that I was fine.

"If that was a quarter-final or a semi there was no way I would have come off but it was more of a precautionary measure and we'll assess it in the next few days."

When Mortlock stayed prone on the turf there were fears Australia could have lost their second key backline player after Stephen Larkham was a late withdrawal with a knee injury.

Five-eighth Larkham will undergo surgery on Sunday morning at the team's French base in Montpellier with an arthroscope to explore damage and also clean out the joint.

Coach John Connolly said a best-case scenario would see the 102-Test playmaker play 10 minutes off the bench against Canada and start in the October 6 quarter-final in Marseille.

In his place, rookie Berrick Barnes starred as the Wallabies jumped to a 22-point half-time lead.

Barnes laid on the first try in the 16th minute with a dart and step 25m out to break the line and then feed Matt Giteau before being hit late and high by Welsh fullback Gareth Thomas.

The 21-year-old, in his first Test run-on start, then slotted a 32m field goal seven minutes later.

He was also strong in defence, saving a second-half try with a desperate ball-and-all tackle on Welsh halfback Dwayne Peel and also snuffing out a dangerous counter-attack as the Reds Dragons fought back.

Barnes looked at home when he kicked off well and then found touch over half-way with a clearing kick with his next touch.

"It was an outstanding effort in the first half particularly in a cauldron like that," Connolly said of Barnes.

"He's a very tough young guy mentally and I thought he showed a lot of composure.

"To nail his first kick into touch like he did, to have enough confidence for the field goal and I thought his defence was good, it was an outstanding debut."

The home side was cheered on by William, Prince of Wales, who was one of 71,022 people in the roofed stadium.

Connolly was pleased with the first-half performance but disappointed by a loss of concentration in the second.

"We lost a fair bit of concentration in the second half I would think and gifted Wales a number of opportunities to come back into the match," he said.

The Wallabies have booked Larkham in for an 8am operation (1600 AEST) and they will know the results at 11.30am (1930 AEST).

The 33-year-old, who was hobbling in Cardiff, felt at worst-case he would not be available until the semi-finals, if Australia wins its quarter-final.

Brought to you by AAP © 2024 AAP