The Red Devils are the early leaders in the Premier League after a four-goal victory over the Hammers at Old Trafford.
Mourinho, however, has said that 'it is just the beginning', and the Portuguese will not allow his side to think too much about the impressive showing last time out.
"It's just the beginning. Last season, we started with three matches and nine points and we finished sixth. So it's not because of a very good first day that I'm going to lose my stability and my discipline and let the players think differently from myself," Mourinho told reporters.
United will look to make it back-to-back wins at the start of the new campaign when they visit Wales to take on Swansea City on Saturday afternoon.