And Mourinho warned Manchester United and Tottenham they cannot afford to fall too far behind the pace.
Mourinho does not believe United and Spurs are out of contention yet though and feels his side, along with current league leaders Arsenal and Liverpool, are also in the title race.
"I don't think we can speak about favourites but we can say that one team is top of the league and some are a little bit far (behind) but I keep thinking that all the six teams are title contenders," he said.
"I keep saying the team with more responsibilities to win it, because their squad is quite unique (sic), is Manchester City.
"Spurs and United know if teams reduce (their points gap) from 10 to seven, or to six, they are again into the race.
"But I think they also know if the move is from 10 to 13, or nine to 12, it becomes hard."
Cesar Azpilicueta has been starting at left-back for Chelsea with Ashley Cole only just regaining fitness after a rib injury, despite the Spain international usually playing on the right side of defence.
Mourinho insists he cannot foresee signing a new left-back in the January transfer window, though, and has urged Cole he may have to remain patient if he is to regain his place in the side.
"Any player that normally starts matches, and Ashley starts matches, for all his career, when they don't I think they are naturally not the happiest guy in the camp," added the Portuguese.
"Professionally, he is always a team player, yes, friend of his friends, yes. So I also can say that he deserves to play.
"But in my opinion, Azpilicueta is doing really well, so it is a question of Ashley to keep working and waiting for his opportunity.
"We are fine. I trust what I have. A left-back with a right foot is not a big problem.
"The market will be open for a month and you never know what will happen but I don't think so."
Mourinho also expressed surprise that striker Romelu Lukaku, on loan at Everton, has stated he may remain at Goodison Park next season.
"Maybe there is a new rule in football, where, when the season is finished, every player is free to decide his future," he said.