Strikes from Emmanuel Adebayor and Carlos Tevez ensured an end to Chelsea's run of five league wins with five clean sheets, while second-placed Manchester United kept up the pressure with a resounding 4-0 win at West Ham United.
"We do not need to have a big reaction because the team is still in a good moment, we showed good play, but it was difficult because Man City played very well," Ancelotti told the club's website.
With Liverpool slumped in seventh place after a dreadful run of form, this season's title chase has become a two-horse race between Chelsea and United, with third-placed Arsenal rank outsiders.
But Chelsea's defeat, which followed a mid-week League Cup quarter-final exit at Blackburn Rovers, albeit for a second-string side, has shown a rare slip in form although Ancelotti remains calm.
"We have two points more than the second team and we don't have reason to be worried," said the Italian, whose side have 36 points from 15 games.
Frank Lampard's first penalty miss since September 2006 and a spurned Didier Drogba chance let City off the hook although Ancelotti felt the home side's goals should never have happened.
"Micah Richards did a handball for their first goal and the second situation for me was not clear because I think Ricardo Carvalho cleared the ball cleanly," he said.
"I am surprised because I consider Howard Webb a fantastic referee with experience, but I don't want to speak more than this because it happened and I want to look forward."
One plus point for Chelsea was the news that the injury which forced captain John Terry off in the match was not serious and the defender should be available next week.
