Wallabies will get better says Cheika
But Cheika acknowledged the tournament will not get any easier as Australia next play Wales. He described Wales boss Warren Gatland as a "master coach."
Australia outclassed England in virtually every area on Saturday night to guarantee their place in the quarterfinals.
The 33-13 score was their biggest winning margin over England at Twickenham. Flyhalf Bernard Foley's 28-point haul was the highest by an Australian against England.
Cheika insisted there is room for improvement before the Wallabies return to Twickenham next Saturday to face Wales to see who tops Pool A, the so-called "Pool of Death".
Australia have beaten Wales 10 times in a row but their coach said a new victory was not assured.
"It is just about ourselves at the moment and trying to improve on that," said Cheika.
"We are coming up against the master coach [Gatland] next week. I'm not going to change what I do because we won a game."
Cheika, the only coach to have guided sides to victory in the European Cup and Super Rugby, said: "There are a lot of areas we can improve on."
"The commitment was very good and we will improve on that going forward.
"We really wanted it, to win and to play well. We knew there would be a lot of pain in England's backyard.
"It was outrageously loud (at Twickenham) and we wanted to get stuck in from the start."
Australia were overpowered at the scrum in losing their last two Tests at Twickenham. But they forced a number of scrum penalties on Saturday and Cheika praised the work of Argentine forwards coach Mario Ledesma.
"Mario has taught me that the scrum is a very important part of the game. You can dominate one but the next one you can get your pants pulled down," said Cheika.
"But you have got to be consistent. Everyone is a threat and we have got to be ready for Wales now."
Australia captain and hooker Stephen Moore also said the team had to "get back to the drawing board for Wales".
The Wallabies lauded their hero Foley.
The double try-scorer said it had been one of the best ever team performances.
"We wanted to put in a performance to make Australians proud, and we delivered," said the flyhalf.
"It's definitely up there and we can take a lot of confidence out of that for next week."
Meanwhile Foley himself saluted the work of Australia back-row forwards Michael Hooper and Scott Fardy who, together with Pocock, pillaged the ball and harried the English throughout the match.
"They put their heads where not many people would want to, and that allows people to do their jobs," said Foley.
"For me it made it a lot easier, but I didn't think it would go that well."
Agence France-Presse
