TWICKENHAM -- Wales lock Alun-Wyn Jones paid tribute to Australia's resolute defensive performance after the Wallabies clinched top spot in Pool A with a 15-6 win at Twickenham on Saturday.

Michael Cheika's side took a six-point lead early in the second half thanks to four penalties from Bernard Foley, but then had to weather an eight-minute spell where they were down to 13 men after Will Genia and Dean Mumm picked up yellow cards.

Wales crossed the whitewash three times in that period but failed to score a try -- with Talupe Faletau guilty of a knock-on and Warren Gatland's side twice held up.

It was a belligerent defensive display from Australia, who were rewarded with a quarterfinal meeting with Scotland next Sunday. Wales will face South Africa the previous day, with both matches back at Twickenham.

"It's the best performance defensively we've faced," Wyn Jones said. "All credit to them and their defensive guys. We crossed the line three times and we should have capitalised, but we didn't.

"I think when you are a man down the time goes very slowly, and when you are man up it goes very quickly -- and that is probably what it looks like. But full credit to Australia. We will look at it and see where we went wrong."

George North, who played centre, added: "We are obviously gutted. It was a brilliant game. Our defence was strong, and there's was strong as well. We left a few tries out there but that is the margins we play with.

"They brought massive line speed in that last block in their 22. I think we could have been a bit smarter in what we did, a bit more accurate and obviously taken our chances."

Wales must now face South Africa in the knockout phase, a team they beat at the Millennium Stadium 12-6 last November.

"I think if you look at their pack they are a bit more physical, a bit more straight-trucking," North said. "But if you look at Australia they have one of the most creative back lines and we coped with them, so we should be okay."

"They are a big bunch of boys," forward Paul Jones concurred. "It is going to be a good test, but we can be confident given the way we've played against them recently."

Should they win, New Zealand likely await in the semi-finals -- with a possible rematch with Australia then on the cards in the final. Despite Saturday's disappointment, the Wales players remain confident they can still win the tournament.

"No-one has ever [won the World Cup] from second in the pool stages but there has to be a first time," Wyn Jones noted. "Hopefully we can do that. If we are to progress where we want to be then we have to beat the best teams."

"It's definitely a tall order, I'm not going to lie, but that is the World Cup isn't it?" North added. "We just have to focus on the next task in hand. There are slightly easier routes to the final but that is the path we've taken and we have to front up for it."