United secured a comfortable win with goals from Marouane Fellaini, Romelu Lukaku and Marcus Rashford.
But despite the big margin, Mourinho claims he was unhappy with the performance of his players following Lukaku’s goal early in the second-half, which put United 2-0 up.
“Three points are important at home. Until 2-0 we were very stable, we played with confidence,” Mourinho said.
“After 2-0 everything changed. We stopped playing, we stopped thinking, we stopped playing seriously, stopped making the right decisions on the pitch.
“We could have put ourselves in trouble, but they didn’t score and we got the third.
“But it was bad decisions, fantasy football, PlayStation football, flicks and tricks. When we stop playing seriously, stop playing as a team, I don’t like it.
“We gambled and you have to respect your opponent. I don’t know if goal difference will play a part. We lost position, our shape, we lost balls in easy situations.
“I didn’t like it, the players relaxed too much.”