Chelsea are a point better off than City after eight games and enter the contest 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," Mourinho said. "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.
"(But) 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."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball