While Mourinho saw his side draw 0-0 with West Ham on Wednesday, City moved top of the table thanks to a 5-1 victory over Tottenham at White Hart Lane.
Manuel Pellegrini's free-scoring side are now a point ahead of Arsenal and three clear of third-placed Chelsea.
Ahead of Chelsea's visit to City, Mourinho said: "Are they favourites? Yes. Are they even favourites to score again four, five, six goals? Yes.
"But the result is 0-0 and we go there to compete and to play."
Mourinho, who won the Premier League twice in his previous stint with Chelsea, has tipped City for the title on numerous occasions this season.
He continued: "For how long have I said the same thing? For how many months?
"For me it is not a surprise but we go there next Monday and the result at this moment is 0-0."
Mourinho's men came out on top against City earlier this season - winning 2-1 at Stamford Bridge in October.
