Cardiff - The Pool A maths are complicated and the permutations many, but hosts England go into Saturday's showdown with Australia knowing defeat means an exit from the Rugby World Cup in the opening round for the first time.
A week after their shock 28-25 defeat to Wales stopped their campaign in its tracks, the hosts must rouse themselves for yet another high pressure encounter at Twickenham.
“It is a huge game,” England coach Stuart Lancaster said on Thursday.
“We respect the quality of opposition but we know we can beat them.”
England have indeed won four of their last five matches against Australia but Lancaster, and his opposite number Michael Cheika, are aware that World Cups are markedly different from June and November tours.
The match (kickoff 1900 GMT) renews a rivalry that has taken in two World Cup finals, resulting in one win apiece, and is traditionally presented as a clash between Australia's backline Cavaliers and the muscle-bound Roundheads of England's pack.
Both teams have moved to augment their traditional strengths and address their weaknesses in the run-up to this tournament, however, and it could be the success or otherwise of those efforts that will decide Saturday's match.
Lancaster has talent out wide and has brought more creativity into his backline with the recall from injury of Jonathan Joseph at outside centre and the relegation of rugby league convert Sam Burgess to the bench.
It is, however, still on the forwards that England will pin their hopes of a victory that would keep alive their bid to win a second World Cup.
Cheika was given a wake-up call when he first took charge of a Wallabies side at Twickenham last year and England showed him that the weakness in the Australian pack was no mere perception but a potentially decisive fact.
He has since overhauled his front five but acknowledges that the success or otherwise of his work can only be properly judged after Saturday's match.
“I know they think we're weak in the forwards,” Cheika said.
“The only place things are going to be different is on the field on Saturday night and that's where we've got to show our colours. Talk's cheap, you know.”
A key confrontation could be in the back row where Australia's world class openside flankers David Pocock and Michael Hooper will take on an England loose trio without a recognised “fetcher”.
England, for their part, will hope the combined muscle mass of Tom Wood, skipper Chris Robshaw and Ben Morgan will help overwhelm the Australians.
Wales and Australia meet at Twickenham in their final Pool A game on Oct. 10, while England take on Uruguay in Manchester later the same day in what the entire host nation, and the tournament organisers, will be hoping is not a dead rubber.
Teams:
England: 1-Joe Marler, 2-Tom Youngs, 3-Dan Cole, 4-Joe Launchbury, 5-Geoff Parling, 6-Tom Wood, 7-Chris Robshaw (captain), 8-Ben Morgan, 9-Ben Youngs, 10-Owen Farrell, 11-Jonny May, 12-Brad Barritt, 13-Jonathan Joseph, 14-Anthony Watson, 15-Mike Brown.
Replacements: 16-Rob Webber, 17-Mako Vunipola, 18-Kieran Brookes, 19-George Kruis, 20-Nick Easter, 21-Richard Wigglesworth, 22-George Ford, 23-Sam Burgess.
Australia: 1-Scott Sio, 2-Stephen Moore (captain), 3-Sekope Kepu, 4-Kane Douglas, 5-Rob Simmons, 6-Scott Fardy, 7-Michael Hooper, 8-David Pocock, 9-Will Genia, 10-Bernard Foley, 11-Rob Horne, 12-Matt Giteau, 13-Tevita Kuridrani, 14-Adam Ashley-Cooper, 15-Israel Folau.
Replacements: 16-Tatafu Polota-Nau, 17-James Slipper, 18-Greg Holmes, 19-Dean Mumm, 20-Ben McCalman, 21-Nick Phipps, 22- Matt Toomua, 23-Kurtley Beale
Referee: Romain Poite (France) – Reuters