No hiding for England
Defeat will see England, who suffered an agonising 28-25 loss to Wales last weekend, become the first world championship hosts to fail to reach the knockout stages.
Australia, two-time World Cup winners, who come into the tournament as one of the most in-form sides with stars such as fullback Israel Folau sense they can beat the English.
"We're obviously aware of what is at stake – you don't have to be a rocket scientist to work it out," said Lancaster who, controversially, was given a contract extension beyond the 2019 World Cup in Japan by the Rugby Football Union last year.
"The fact is that if we don't win on Saturday then we won't go through from the pool stage.
"I understand the consequences, I understand the accountability and responsibility for delivering in this World Cup, 100 percent. There's no hiding away from it."
He added: "The picture would be completely different on Saturday night after a win. The old analogy that a week is a long time in sport is absolutely true in this case."
England, changing their midfield line-up yet again, have recalled Jonathan Joseph at outside centre after he missed the Wales defeat with a chest injury.
Owen Farrell again starts at flyhalf after a flawless goal-kicking display against the Welsh and Lancaster has backed the player after some scathing criticism.
"Owen Farrell's performance against Wales was excellent. He gave us what we were looking for – his defensive strength and qualities but his kicking game was excellent," Lancaster said.
"There's a black and white assumption people have made that if George Ford plays we play fantastic, creative, attacking rugby and when Owen Farrell plays we don't. I don't subscribe to that view personally."
Up front, No.8 Ben Morgan and lock Joe Launchbury start in place of the injured Billy Vunipola and Courtney Lawes respectively.
England prop Joe Marler has found himself in the spotlight this week after Bob Dwyer, coach of the Australia side that beat England in the 1991 World Cup Final, accused him of scrummaging illegally.
"I think our scrum has been good, honest and excellent across the last three years," he said.
Australia, who won this year's southern hemisphere Rugby Championship, boast an array of backline talent including Folau, playmaker Matt Giteau and scrumhalf Will Genia.
Wallabies coach Michael Cheika has tried to insist that England, who've won last two Tests against Australia on the back of a powerful forward effort, believe his side have a "weak" pack.
"No I don't," said Lancaster. "They've improved but I think we can put pressure on them. They've got two very, very good breakdown experts [Michael Hooper and David Pocock]."
Cheika, who on Thursday named the same team that beat Fiji 28-13 in Australia's opening game, said: "They (England) have done it to us, they've stuck it to us [in the pack] the last couple of times so there's nothing we can say in our room that's going to make any difference.
"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".
Several England players have suggested Saturday's match is now their 'World Cup Final' but Cheika said: "It is tournament play. I dont think you can all of a sudden decide 'it's the final, we had better play'."
Agence France-Presse
