Mourinho's men claimed a second successive four-goal win in the league, as goals from Eric Bailly, Romelu Lukaku, Paul Pogba and Anthony Martial ensured a hard-fought win for the Red Devils at the Liberty Stadium.
"During almost 90 minutes - I don't say 90 because there was a moment when they had a chance and we lost a little bit the confidence - they were waiting with class, calm and consistency for the moment to kill the game," Mourinho told BBC Sport.
"Swansea played with five in the back and they had a moment when they felt they had to change and when they did we had more space and killed the game.
"I felt in control, if you had a chance to look at me and my body language I think you could see that. Football is football and when you make a mistake you can concede so I never felt totally relaxed. I had players on the bench who could help me.
"Happiness in our play. It happened to me so much with my teams, you winning 1-0 and you can can concede. There was no need to close the door, just let the horses run freely. Anthony Martial is working hard. He is confident. The French language connection is there to help him a lot and get to the level we know he can be because the potential is huge."
Victory over Swansea has seen Mourinho's United maintain a perfect league record with two wins out of two.