Pep Guardiola's side registered a top-flight record 15th league win in sequence on Wednesday, thrashing Swansea City 4-0 while United were flailing in their attempts to see off Bournemouth.
Romelu Lukaku's goal was enough to beat the Cherries 1-0, United responding to their derby defeat, and Mourinho afterwards admitted his players were showing signs of fatigue.
When asked about the title race, he told BBC Sport: "We play match after match and the next we have to try to win. We have a difficult one at West Brom and we try match after match.
"It is only over in May. If it is over now I go on holiday to Brazil or Los Angeles."
When asked whether his side had suffered a hangover from their 2-1 defeat to City, Mourinho replied: "Fatigue, yes, but hangover - no.
"The game was a big one, and a defeat does not help in your recovery - victories help, defeats don't.
"They were difficult opponents and difficult conditions. If we had scored the second it would have been a calm night for us."
Lukaku scored his first Premier League goal in five matches after 25 minutes to give United the lead against Bournemouth and that proved to be the difference between the two sides.
"I am pleased with the three points, it was difficult match," Mourinho continued. "They had one more day's rest than us, they were fresher than us, and mentally fresher because a big match takes more from our players.
"We had chances, [Anthony] Martial missed a good chance, [Marcus] Rashford could have had an astonishing effort, and in the last 15 they pushed us."
United's Luke Shaw started at left-back after being named among the substitutes against City, and was replaced in the 83rd minute by Ashley Young.
When asked whether Shaw is his first choice in the position, Mourinho replied: "I'm not saying first or second choice, he's an option. His history is an incredible injury and more surgery at the end of last season.
"He needs competitive matches, we gave him that and he had some cramps so we had to change him. The standing ovation for him I liked, it helps the player."