England captain Martin Johnson believes England will have to drastically improve to progress past the quarter-finals after their 35-22 win over Samoa.
Johnson was impressed by Samoa's play
The Pacific Islanders surprisingly outplayed the English for much of Sunday's game at Melbourne's Telstra Dome, before England's superior fitness paid off.
And Johnson said: "At this rate we're not favourites to win next week [against Uruguay on Sunday], let alone the quarter-final.
"We have to look at ourselves as we're not good enough. There were too many mistakes again from us."
Samoa enjoyed more than 90% of possession in the game's opening 10 minutes and went ahead through a Semo Sititi try.
Fly-half Earl Va'a kept them ahead with some precise kicking, which kept his team within a point of England with only 10 minutes remaining.
In the end, late tries from Iain Balshaw and Phil Vickery ended the contest.
Afterwards Johnson was full of praise for the Samoans.
He added: "I thought they played fantastically well. There was only one team on the park for 20 minutes and we didn't even touch the ball for 15 minutes.
"They played great - all credit to them. They could have beaten us.
"They deserved a try and played really well. We came back and battled in the second half. I thought we would come through to win."
England coach Clive Woodward admitted he was a relieved man after seeing his side finally edge the game.
Woodward said: "It was a major scare. But the only team who did not underestimate Samoa was England.
"We had to be at our best and I thought the guys did brilliantly well to come back. But well done to Samoa."