Argentina's last-eight place could be confirmed on Friday if Tonga fail to pull off the unlikeliest of bonus-point wins over New Zealand in Newcastle. The Pumas play Namibia two days later.
Scotland have a potentially trickier task, needing victory over dangerous Samoa on Saturday to grab second spot in Pool B and end Japan's entertaining World Cup challenge before they face the United States in their final pool game.
"For a lot of us this is going to be the biggest match of our careers," Scotland number eight David Denton said as the team welcome back fit-again flyhalf Finn Russell.
"For most of the people on our team this is our first World Cup, but now we've essentially got a playoff game."
Australia against Wales at Twickenham on Saturday will decide which team top Pool A and avoid twice champions South Africa in the last eight as well as a potential semi-final against the All Blacks.
Wallabies coach Michael Cheika has stuck with two open-side back-row specialists for the Wales showdown, bringing in Sean McMahon for the suspended Michael Hooper while the experienced Drew Mitchell replaces injured winger Rob Horne.
Fullback Israel Folau, who rolled his ankle in last weekend's 33-13 victory over England, was cleared to start after successfully coming through training.
Wales have also opted for two open-side flankers, with Justin Tipuric joining captain Sam Warburton. Winger George North starts at outside centre as the Welsh look to end a 10-game losing streak to Australia stretching back to 2008.
"We aren't having to desperately win the game to reach the quarter-finals. But win this group and potentially the route through to the quarters, semis and finals is easier than the other side," Wales coach Warren Gatland said.
The weekend's other key game that will finalise the shape of the quarter-finals takes place in Cardiff on Sunday when France and Ireland meet to decide Pool D and who gets to steer clear of reigning champions New Zealand in the last eight.
For eliminated hosts England, the tortuous build-up to Saturday's dead rubber against Uruguay drew to a close as coach Stuart Lancaster was forced to play down a training ground bust- up between his assistant Mike Catt and flyhalf Danny Cipriani.
Lancaster said it had taken "some work" to get everybody focused for the game while lock Joe Launchbury was as uncomfortable talking about his man-of-the-match award against the Wallabies as he was accepting it at Twickenham.
"The word 'embarrassing' comes to mind," he said. "It certainly won't be going on the mantelpiece, that's for sure.
(Editing by Ed Osmond)
