Chelsea welcome City to Stamford Bridge a point better off after eight games and on the back of a seven-match unbeaten run which has included 14 goals in their last four games.
"We have to play our game," said the Portuguese boss. "We are going to play our game and let's see if our game is enough to win against them.
"I just play every game the same way. We want to win. To win is good, to lose is not good.
"In this moment, with the way the Premier League is going week after week, no result will put a team in a great situation, no result will put a team in a difficult situation.
"Every weekend somebody loses points. Some weekends more than one of the top teams lose points.
"The league is hard, so I don't think at this stage, mid-October, one game is going to be crucial.
"We have tests every week. It's a big team, yes, it's a very good team, but every match is a test and every match is three points."
Mourinho believes six teams are in title contention, including Manuel Pellegrini's City.
"He has the most important thing which is an unbelievable squad of players," added Mourinho, who also maintains Manchester United are still in the running, despite already being eight points behind leaders Arsenal.
"They had lots of difficult matches and other teams, they didn't," added Mourinho.
"They played already against Chelsea, they played against Liverpool, they played against City.
"There will come a time and a period of fixtures where they will win consecutive matches and where other teams will lose points and where they will close the gap and where they will put themselves in a position to fight for the title."
Chelsea v Manchester City is live on Sky Sports 1 HD on Sky Sports 1 HD