Striker aware that the Red Devils will need to be firing on all cylinders to take the points against their title rivals and highlights Juan Mata and Daniel Sturridge as threats
The Red Devils have begun the campaign with some dazzling performances against the likes of Arsenal and Tottenham Hotspur, but the England international remains wary of the threat posed by Andre Villas-Boas' side.
"The Chelsea game's going to be difficult and we need to be at our best," Rooney told the club's official website.
"Obviously Arsenal are always difficult but with the injuries they had when they came to Old Trafford we were the favourites to win that one."
The summer signing of Juan Mata from Valencia and the return of Daniel Sturridge to Stamford Bridge after a loan spell at Bolton Wanderers has added a new dimension to Villas-Boas' team but Rooney remains confident that United are well-equipped to deal with those threats.
"They’ve got a few new players – I saw Daniel Sturridge started the last game and Juan Mata played as well," he said.
"I’m sure they’ll have a few new ideas to go along with the new signings they have, but I'm sure we’ll be able to cope with that.
"This is going to be another big game and if we can win we’ll go five points clear of Chelsea and keep our winning run going at the start of the season."
Like many of the United squad Rooney has cited the influx of young players such as Phil Jones and Danny Welbeck as a big factor behind the club's impressive early season form.
"I worked extremely hard during pre-season and the manager's lobbed a few of the younger players in and it’s worked well for us," he said.
"Obviously I’m benefiting from that, with goals. There’s a lot of energy around the team – it’s going great for us at the minute."