England closed the day out with a scrappy 19-7 win over France - but were one of only two nations, along with pre-tournament favourites South Africa, to head into the last eight unbeaten.
Head coach Mike Friday assembled a new-look squad for this weekend, featuring eight new caps, and he warned England must improve before facing the Aussies.
"We have actually lost to Australia the last two times we faced them," said Friday.
"There were two or three mistakes against France where a more experienced side would have really punished us.
"But these guys have to go through the learning experience. We will talk about the consequences of our actions this evening and make sure we can rectify them tomorrow.
"Day one is all about getting a ticket to the ball game. We have our ticket and we are playing Australia, which will be a very tough game."
The Australian team was only pulled together a week ago after the original squad were axed after threatening to strike over a pay dispute.
But they booked their passage in the most dramatic fashion. Having been stunned by Portugal in the opening game they bounced back to beat Kenya and then world champions Fiji with the last play of the game.
Friday added: "They will be buoyant after beating Fiji, they will be high on confidence and they will think we will be there for the taking.
"They have beaten us on the last two occasions but the form book goes out the window."
Scotland edged Zimbabwe 19-17 but finished bottom of Pool B after losing to England and France. Wales produced one of the big results with a 17-14 victory over Samoa - but Dai Rees' men were ultimately disappointed after being edged out of the Cup competition on points difference.
Samoa bounced back to beat New Zealand and the islanders sneaked second place in Pool D, relegating Wales to the Bowl competition where they will face Argentina.
The same thing happened to Wales in George last season, when Argentina beat the All Blacks, but Rees is determined his men respond by bringing home some silverware.
"We have been there before so we knew nothing was assured. We couldn't have done any more," said Rees.
"There are eight new guys and the learning curve has been huge. There have been a lot of zero scorelines here and we created enough to score two tries against New Zealand and learned enough to transfer it into the game against Samoa and come away with a narrow win.
"These guys are loving every minute of it and our simple focus now will be to go home with some silverware. We did that at every tournament we entered last season."
Newport Gwent Dragons flay-half Aled Thomas has caught the eye for Wales - and Rees is delighted with the way he stepped up today.
"A few people have questioned Aled's ability but I think he is proving he is a quality player," said Rees.
"He hasn't got the same kind of skills as James Hook in terms of his step and his out-and-out pace, but he is a different kind if playmaker.
"He has an ability to beat players and offload to create space for players around him. He has stood out and is one of the guys to come through."