LONDON (AP) -- It was the loss which Michael Cheika so eloquently described as a boot to the backside that is driving his Wallabies at the Rugby World Cup.
From Warren Gatland's perspective, it's a streak of 10 losses that is serving as motivation for his Wales squad ahead of Saturday's Pool A decider against Cheika's Australians.
Both teams are into the quarterfinals with three wins apiece, including victories over England that ensured the host team will not feature in the knockout stage.
First is foremost, though, for both coaches. The winner of Pool A avoids two-time champion South Africa, the Pool B winner, in the quarters.
The Australians have lost just one test in 2015, a heavy 41-13 defeat to the All Blacks at Auckland in August, a week after clinching the Rugby Championship title with a 27-19 win over New Zealand in Sydney.
Asked what kind of momentum the two-time champion Australians had built, Cheika's response was short and to the point.
"None," he said. "We supposedly had momentum after we beat New Zealand. And then they put their boot to our backside. That can happen if you are not 'on' every day. We have to learn from those times."
The Welsh has lost all 10 tests to Australia since 2008, and 22 of the last 25 dating to their upset 22-21 win over a 14-man Wallabies lineup in the bronze-medal match at the first Rugby World Cup in 1987, but Gatland is focusing on the fact they've been getting closer. The last five games have been decided by five or fewer points.
"We are desperate to win this game, as win this group and potentially your road through to quarters, semis, and final is a little bit easier," he said. "The last five times against Australia there has been a score in it. We've been ahead in games and not been able to finish it off -- you learn from that, and experience comes from that."
Gatland predicted a "fierce contest" at the breakdown after selecting two openside flankers in his starting lineup in a slight variation on Australia's plan.
He shifted skipper Sam Warburton to the blindside flank to make room for Justin Tipuric on the openside of the scrum, and retained Taulupe Faletau at No. 8.
Cheika opted for Sean McMahon to replace suspended flanker Michael Hooper in a like-for-like selection. He kept David Pocock, arguably the game's best fetcher, at No. 8, and Scott Fardy on the blindside flank.
"It is going to be a massive battle and pretty painful," Cheika said.
Israel Folau passed a fitness test on his ankle and will start at fullback for Australia, with Drew Mitchell starting on the wing in place of the injured Rob Horne. In the only other change to the Wallabies' starting lineup that beat England 33-13 last weekend, Dean Mumm will start at lock and Rob Simmons moves back to the bench.
Gatland made six changes to the team that beat Fiji, including moving George North from the wing to partner Jamie Roberts in a big, powerful center combination to target Australia's smaller midfield.
Fullback Gareth Anscombe -- added to the squad when the Welsh injury toll escalated -- was in the starting XV for the first time in a new back three combination with Alex Cuthbert and Liam Williams.
With four natural No. 7s on the field, conditions will be difficult for the form halves pairings of the tournament. Welsh halves Gareth Davies and Dan Biggar have exceeded all expectations, while Will Genia and Bernard Foley have directed the Australian attack.
Biggar and Foley each played starring roles in wins over England, with the boot and in general play. Biggar kicked 13 goals from 13 attempts against England and Fiji.
Genia said Davies had been one of the best scrumhalves in the tournament, and Biggar's boot made it dangerous to concede penalties anywhere beyond halfway.
"We know they are a very good side and if we are little bit off, we will be punished," Genia said.