The Red Devils kicked off their 2017-18 Premier League campaign with a resounding victory over a poor Hammers side, earning the win through a Romelu Lukaku brace and goals from Paul Pogba and Anthony Martial.
West Ham came close to pulling one back with the score at 2-0 when Marko Arnautovic flicked a header onto the top of the crossbar, but the visitors offered little else in an attacking sense and were comfortably brushed aside.
Speaking to Sky Sports News after the match, Mourinho said: "The game was difficult, it was open at 2-0 and they had a chance to score. It was not a 4-0 game. When you relax, you play with confidence. We did not start especially well, we looked nervous but then we put in a quality performance.
"A word that I like is confidence, they played with confidence and played football. It was a very positive performance. The fact we start winning and are top, it means nothing. The performance and the levels of confidence is what means a lot to me.
"We lost two points against them last season and had similar games where we were dominated. Today we got the three points. The reality is that in the last part of the game, instead of being boring and controlling the game, we scored a third goal and we could enjoy it."
United, who top the Premier League table on goal difference after one game, return to action next weekend with a trip to take on Swansea City.