Heading into their first derby of the season on Sunday, United hold a three-point lead over second-place City. Chelsea, who play Sunderland on Saturday, are seven behind City.
London: Despite winning the Premier League title last season, Manchester City still have a sense of inferiority heading into Sunday's derby with United.
City have emerged as a force over the last two years, with more than a $1 billion of investment leading to their first English league title in 44 years. But United remain the clear global power after winning a dozen Premier League titles since 1993.
And, heading into the first Manchester derby of the season on Sunday, United hold a three-point lead over second-place City.
"They are better than us at this moment," City manager Roberto Mancini said Friday. "We have only been here for two years. They are used to playing these games in the title race for 20 years. They have won everything for 15 years.
"You can't change this in two or three years. You need more time."
City, though, beat United twice in the league last season and claimed the title on goal difference, helped by a huge victory at Old Trafford.
"The derbies had a big impact (last season), particularly that 6-1 defeat, on goal difference," United manager Alex Ferguson said. "That's what cost us."
Neither United nor City have really impressed this season, and they have established themselves as front-runners in part due to Chelsea's slump.
City are unbeaten after 15 games but have drawn six of those. United have been relying on their powers of recovery to sit at the top with seven of their 12 wins recovered after falling behind first.
"I am sure City will be working on set pieces because I think we've lost something like 10 goals from set plays this year, which is a lot," Ferguson said. "We're hoping to find a solution and we're hoping a solution makes a difference."
The Manchester derby has established itself as the biggest fixture in the English football calendar, displacing United's matches with Liverpool.
"Liverpool and United games over the last 25 years have been unbelievable," Ferguson said. "They've always been the most important games. It's shifted because at this moment Liverpool aren't challenging for the league like City are.
"City are our biggest threat and we're their biggest threat, so that's changed. Their fortunes changed the minute Sheikh Mansour (bin Zayed bin Sultan Al Nahyan) took over (in 2008) ... we have to accept their challenge like we did when Chelsea came along."
Chelsea, the 2010 league champion, appeared to be resurgent this season after winning the Champions League. But after leading the way in the opening weeks of the season when Roberto Di Matteo was in charge, the Blues fell back and Rafa Benitez was brought in as a replacement.
After seven league games without a win - three under Benitez - Chelsea are in third place only ahead of Tottenham on goal difference and seven points behind second-place City.
Before flying to Japan for the Club World Cup, Chelsea are at Sunderland on Saturday, reeling from being the first Champions League holders to exit at the group stage on Wednesday.
"I don't know what's gone wrong ... the players have been asking that question themselves and we don't know really," Chelsea defender Gary Cahill said. "Where do you point the finger? It's obviously stuff you need to work on in the training ground. It's the same group of players who started the season beating teams and scoring goals and keeping clean sheets."
If Chelsea slip up again on Saturday, Tottenham could rise to third with a victory at sixth-place Everton on Sunday.
Arsenal have fallen to 10th, while Saturday's opponent West Bromwich Albion are riding high in fifth.
"Let's not go overboard," Arsenal manager Arsene Wenger said. "We have 24 games to play. We are in all the competitions, what many clubs would love to (be), so it is down to us to make the season right and to turn the season around well on our side."
Queens Park Rangers are last and still without a win as the team heads to Wigan on Saturday.
Southampton and Reading, the two other sides in the relegation zone, meet on Saturday, when Aston Villa also face Stoke and Swansea take on Norwich.
On Sunday, West Ham host Liverpool, and the following night Newcastle are at Fulham.