The Red Devils cruised to an impressive 4-0 win at Old Trafford last weekend, with Romelu Lukaku scoring twice on his home debut before late goals from Anthony Martial and Paul Pogba.
With champions Chelsea having suffered a shock 3-2 home defeat to Burnley, Liverpool drawing 3-3 with Watford and Manchester City and Arsenal having to battle to three points, some have already identified United as the most likely to be at the top of the table at the end of the season.
However, manager Mourinho insists his side have not become a "dream team" simply by beating the Hammers.
"I'm too stable and too experienced to lose my discipline, to lose my stability and to think that a 4-0 result makes us the best team in the country, the favourites, the dream team," he told a news conference ahead of Saturday's clash with Swansea City.
"We are not favourites, not the dream team. We have more confidence than last season, probably more happiness, [we're] more relaxed on the pitch. But I'm calm.
"When I won two consecutive titles with Chelsea [in 2004-05 and 2005-06], the United manager [Alex Ferguson] said we brought the bar to a certain level and that they had to improve a lot to try to win the trophy back. I think this happens every season.
"Somebody wins and the others are not happy. They don't accept it with their hands in their pockets and the others improve to try to be better."