Folau admitted his ankle was "pretty sore" after struggling to find his best form in the first half of the Wallabies' 15-6 win against Wales.

But the fullback found his feet in the second half despite the anguish on his face and managed a try-saving tackle and a slicing run that almost sealed the result for Australia.

He faces a race against time to recover to play against Scotland in the quarter-final at Twickenham on Sunday (Monday morning AEDT).

Wallabies coach Michael Cheika wanted to substitute his star in the dying minutes, but there were no reserves left on the bench and Folau had to play through pain.

"Yeah, it was pretty tough. Me personally, I'm pretty sore, the ankle is a bit sore," Folau said. "But besides that, it's pretty satisfying to have a win like that. I expected it was going to be sore, so I just have to manage it and hopefully it will be sweet. I will do everything I can to make sure I am right for the game. It's a big game … you don't want to miss those games. I'm pretty confident I will get through."

The Wallabies face fresh injury concerns with David Pocock limping off with a calf problem and Matt Giteau appearing to reinjure his ribs.

Giteau and captain Stephen Moore will be playing their 100th Test in the clash against Scotland if both wake up unscathed.

The Wallabies will also be bolstered by the return of Michael Hooper after serving a one-match suspension. The back row is one of the Wallabies' strengths but Hooper's absence, Pocock's injury and a substituted Sean McMahon forced Scott Fardy to play openside flanker for 20 minutes.

"It's great to see guys play through pain for the other guys in the team, there's a lot of respect for them," Fardy said.

"We've got depth in the back row, that's a real confidence builder for us going forward. I was pretty knackered a bit further behind the play than Poey [when I shifted to openside flanker].

"But I've got no doubt if guys come in they will do the job when they're called on."

The players have been buoyed by one of the most courageous defensive efforts in recent Wallabies history.

They were down to 13 men for 10 minutes when Will Genia and Dean Mumm were sent to the sin bin, but managed to withstand a Welsh onslaught to hold on for a historic win.

Folau was called on in a one-on-one battle with giant Wales centre George North as they pushed for a game-changing try.

But two years after North embarrassed Folau in the British and Irish Lions series by carrying Australian rugby's most prized possession on his back as he ran with the ball, it was Folau's time for revenge.

He brought North down to ground and Kane Douglas then backed it up with a try-saver of his own as the Wallabies clung on to a narrow lead.

"It showed how much work we put in together and how much respect we have for each other," Folau said.

"We had no option there but to dig really deep at that stage where we had two guys off and only had 13 players. We really had to test ourselves.

"It was about belief and the care you had for the bloke beside you. And that's what we have been trying to build in this environment."

The Wallabies have secured a spot on the perceived easier side of the World Cup draw. They play Scotland in the quarter-final with a semi-final against Argentina, France or Ireland. They also avoid two-time champions South Africa and defending champion New Zealand until a potential clash in the final. But the Wallabies are refusing to look beyond Scotland.

"We can get a lot of confidence out of that but we also have to keep working hard and stay humble," Folau said.