The Citizens' 3-1 victory over Tottenham Hotspur on Saturday meant that the Red Devils had to avoid defeat against the league's basement side on Sunday to keep the title race alive.
Mourinho criticised his players for the "difference in attitude" from last week's 3-2 derby win, but also disputed the narrative that United's loss to Albion is what handed Man City the title.
"I won eight titles and I am not on the moon because I won against Manchester City," the Portuguese told Sky Sports News.
"I saw lots of people on the moon because we won against City. You could see the difference in the attitude to players compared to last week. We deserve to be punished, but the defeat was too heavy.
"I have won titles, I would not be happy if someone said the title was won if someone loses a match. City won the title because they won more points than everyone else, not... because United did not win, it is not fair on them."
Man United sit just one point above third-placed Liverpool, with fourth-placed Tottenham Hotspur a further three points behind.