By Bryn Palmer
BBC Sport in Lens
England are banking on the imminent threat of South Africa to stir them from their World Cup torpor.
Rees is hoping England will rise to the task against South Africa
Captain Phil Vickery said the England dressing room was "like a funeral" after Saturday's 28-10 win over USA.
And flanker Tom Rees told BBC Sport: "It didn't feel like we had won but that is good because it means the guys are not happy with the way things went.
"There were flashes there, but the big things are still lacking and hopefully a big game will bring it out of us."
Rees, like head coach Brian Ashton, identified England's lack of physicality at the tackle area as the main area of concern before Friday's crucial pool clash with South Africa at the Stade de France.
The winners of that game are likely to top the group, although Samoa and Tonga will also present a threat to England if their opening display was anything to go by.
"We lacked a bit of composure and the breakdown was a problem area for us, and we have to look at the reason why," said number eight Lawrence Dallaglio.
"The fear of failure will be there against South Africa and perhaps that will give us the extra edge in physical situations to up the ante, but it is more mentally in the way we approach the game.
"We have to accept that from one to 15 the energy and intensity against the USA was not up to the level we would expect."
Ashton insisted there is "no point dwelling on what happened" against the Americans, given that the Springboks will present a "completely different" challenge.
But given his pre-match insistence that England needed to "hit the ground running" in order to build confidence for the South Africa clash, Saturday's lacklustre display was hardly what he had in mind.
I don't know whether I've done enough to stay in the team
The head coach stressed his primary task this week will be to ensure his players are mentally prepared for the onslaught they can expect from a side ranked number two in the world.
"We already did our analysis on South Africa a few weeks ago, and now we need to get the right players on the field to play the way we want to against them," he added.
"Physically it won't be a heavy workload this week, but mentally there is a bit to do. But playing against the green and gold of the Springboks usually sharpens the senses."
Ashton has decisions to make at centre, fly-half and number eight in particular after Saturday's performance.
The positions of Jamie Noon and Mike Catt will come under scrutiny, as will that of Dallaglio, while Jonny Wilkinson's fitness or otherwise will be determined in the next 48 hours.
Wilkinson is now off crutches in his recovery from a twisted ankle but is still a major doubt, meaning Olly Barkley, man-of-the-match against the Americans, will almost certainly retain the number 10 jersey.
"I am happy with what I did but whether you play at eight, nine, 10 or 12 you are in charge of the game, and there were errors in organisation and control," Barkley said.
"I don't know whether I've done enough to stay in the team. My mindset going into the game was not to let the side down in my first World Cup game.
"I wanted to play well for myself and the rest of the team, and I would love to start against South Africa, whether it is at 10 or 12. But we will have to wait on Wilko's fitness and see what happens after that."
Dallaglio thinks Barkley has proved he is an asset to England.
"Olly has stepped in there and taken his chance very well," said the Wasps veteran.
"Hopefully Jonny's rehabilitation from his ankle injury will continue, but Olly has put his hand up and said he is going to be there or thereabouts for the rest of the tournament."