"Their players are obviously very good and their manager (Manuel Pellegrini) is also doing a good job," Mourinho told a news conference on Friday.
"On top of that, and this is just pure coincidence, the reality is they have had many crucial decisions in their favour.
"They were lucky against Liverpool, against Newcastle and against Tottenham. But I repeat this is just pure coincidence."
Fortune certainly favoured City on Wednesday when they romped to a 5-1 league win at White Hart Lane after Tottenham defender Danny Rose was sent off for a clean tackle early in the second half that prompted the referee to award a penalty.
Rose has since had his red card rescinded by the Football Association.
City, who have been banging in goals left, right and centre all season, will be without leading scorer Sergio Aguero on Monday.
The Argentine has been ruled out for a month after sustaining a hamstring injury at Spurs.
Mourinho said it would hardly matter because Pellegrini has an embarrassment of striking riches at his disposal.
"City score goals and I don't think for them it is important if somebody is injured," added the Portuguese.
Third-placed Chelsea, surprisingly held to a 0-0 home draw by struggling West Ham United on Wednesday, will slip six points behind City if they lose on Monday but Mourinho said his players would go all out for victory.
"We are not going to change our philosophy," said the Chelsea manager.
"We are going in a certain direction and just because we are playing a certain opponent doesn't mean we are going to change that. We are going to try to win."
(Writing by Tony Jimenez; editing by Ed Osmond)
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