Joe Launchbury has admitted that England will have to find another level after kicking off the World Cup campaign with a 35-11 victory over Fiji at Twickenham.
Despite dominating in the first half, the hosts struggled to hit the same heights after the break before eventually pulling away in the closing stages to earn a bonus point.
With Wales, Australia and Uruguay to come in Pool A, Launchbury is fully aware that Stuart Lancaster's side must improve to stay on course for a spot in the quarter-finals.
"They're a great team. I genuinely believe that if they play with that fight and that passion, they are going to get an upset in this group. They are a strong side with great individuals so we always knew it was going to be tough," the Wasps lock, who came off the bench in the second half, told Sports Mole.
"Our goal now has to get better. We are not completely satisfied with our performance. We know there is areas of our game that we need to improve, and that is the real challenge for us now. We have to get better each week."
England host Wales at Twickenham next Saturday.
