The hosts raced to a surprise 2-0 lead with goals from Aaron Mooy and Laurent Depoitre in the space of five first-half minutes and although Marcus Rashford was able to halve the deficit in the closing stages, United were unable to salvage a point as they fell to defeat at the hands of the newly-promoted side.
The result saw United fall five points behind league leaders Manchester City and, speaking after the final whistle, a downbeat Mourinho revealed that he was "surprised" by what he had witnessed.
"The team that wanted it more won. When the best team wins there is nothing to say," he told reporters. "I don't know why they wanted it more. I won't be critical of my players in the media. I will analyse the game and, if I need to, I will criticise them.
"I was surprised by our performance, I was not expecting that. The team that started with emotion, aggression, intensity and desire, the team that played the game of their lives was the team that won. Maybe in the second half we wanted it a little more and maybe we could get a draw, but I honestly think we deserved the punishment of the defeat.
"I'm disappointed, but the reality is they were stronger than us. I prefer to be at peace with football and to be at peace with football is when the best team wins.
"The mistakes we made can't be taken out of context. The context was that the first-half performance opened the door for mistakes to be made. It would be unfair to point fingers at players for individual mistakes. They were a consequence of what happened in the first half. A bad team deserves to be punished."
Next up for United is a trip to Swansea City in the EFL Cup on Tuesday night, ahead of a home encounter with Tottenham Hotspur in the league next weekend.