Chelsea will be watching the Manchester derby closely on Sunday as a draw or a win for United would put the London club just one point off the pace at the top of the Premier League - if they can beat Queens Park Rangers in a derby of their own.
For all the Manchester clubs' impressive early-season form, Chelsea sit just three points behind going into Sunday's games.
Despite questions marks over Fernando Torres's form and Frank Lampard's role in the team, Andre Villas-Boas's side have quietly started to motor. They have netted 13 goals in their last three games, including a 5-0 demolition of Genk in the Champions League on Wednesday.
The Portuguese manager goes into Sunday's game against London rivals QPR with a weight of options to choose from, and he has one eye on the Manchester clubs above his side.
"We want to continue to compete to try and overtake them as soon as possible," Villas-Boas said. "We have to get on with it. We just want to be top at the end of the season."
Villas-Boas added: "We have to keep winning and wait for something like last weekend.
With a gap beginning to open up between the top three and the rest, some have written off the title challenges of the chasing pack.
But Petr Cech, the Chelsea goalkeeper, concurred with his manager's assessment.
"Everybody's talking about the two Manchester teams and us," he said. "But I think you can't forget Liverpool, you can't forget the others, because this is a tough league and there's a long way to go.
"So let's see another set of 10-15 games. After Christmas, we can speak about this again."
United and City's sensational starts to the season have meant Chelsea have been more under the radar than they are used to.
Cech added: "We are focused on our jobs, our training, our work.
"People can talk about Manchester or the other teams.
"Even if you're in the spotlight and everyone's talking about you, your main target is to keep your feet on the ground, to work well, to improve and to do your job. I think that's what we've been doing so far and you can see we are in a good position in the league and a very good position in the Champions League.
"So far, it's been very good for us."
Neil Warnock's QPR failed to beat bottom side Blackburn Rovers last week and were hammered 6-0 by fellow strugglers Fulham two weeks previously, but the manager is not fazed by the prospect of another tough afternoon on Sunday.
"You know what you're going to get with Chelsea and you just have to hope they have an off day," Warnock said. "They're such a good team. We just have to get the atmosphere and enjoy it, give them a good game if we can."