The contest is one of the most eagerly awaited of the season so far, pitting squads lavishly assembled by Roman Abramovich and Abu Dhabi's Sheikh Mansour, one of the few men in the world with more disposable cash than the Russian oligarch.
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."
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," Mourinho said.
One of the key figures in the City squad is Yaya Toure, who has had a fraught week after being subjected to alleged racist abuse in his side's Champions League win at CSKA Moscow.
On the field, former Barcelona midfielder Toure gives City "everything", Mourinho says.
"Fantastic player," the Portuguese added.
"He gives them everything. Leadership, defensive work, attacking work, goals, set-plays, physicality, experience."
Pellegrini preceded Mourinho as Real Madrid boss before being revived by a spell at Malaga.
Mourinho insisted he has had "no problems" with the Chilean ahead of their first meeting in English football.
The self-proclaimed Special One will be in the opposing technical area to Pellegrini on Sunday after paying an B£8,000 fine and avoiding a touchline ban for his dismissal during last Saturday's controversial defeat of Cardiff.
Mourinho still disagrees with his dismissal, believing a ticking off would have been sufficient, in a similar manner to warning a player by issuing a yellow card.
"I was not offensive, I was not aggressive, I was not non-polite," Mourinho said.
"I didn't use bad words, just a way to express that I was not happy with what was going on. That's fine. I paid the fine and I can work on Sunday.
"I think the sending off is more unfair (than the fine). If I'm punished to break the way I have to behave in the dugout, and I pay a fine for that, I think that's fair.
"What I think is unfair, it's not a reason to be sent off."
The cash-injection renaissance of City has echoed Chelsea's.
Mourinho led Chelsea to a first championship in 50 years in 2005; City won their first in 44 years in 2012.
City were described as noisy neighbours by Sir Alex Ferguson, the former Manchester United manager whose autobiography was published this week.
Mourinho was one of the few to avoid the wrath of the Scot and would not comment on Ferguson's claim that Chelsea midfielder Frank Lampard is not a world-class player.
"I don't want things out of context," Mourinho said.
"I'm very interested, but I want to read the book. I don't want other people to read the book for me."
Mourinho maintains David Moyes' United are still in title contention, despite already being eight points behind leaders Arsenal.
"They had lots of difficult matches and other teams, they didn't," Mourinho said.
"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."
Mourinho has no fresh fitness concerns, with left-back Ashley Cole available again following a rib injury.
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