Romelu Lukaku scored the second goal in the 53rd minute of the 3-0 win, and United could only add the third in the 84th minute.
Following the game, Mourinho said that his players started playing 'PlayStation' football following Lukaku's goal in the game.
"We made bad decisions," said Mourinho.
"Fantasy football, PlayStation football, tricks - and when you stop to play as a team and when you stop to play seriously, I don't like and you gamble a little bit.
"Probably the players felt that the game was under control with the 2-0 lead, but football is football and you have to respect your opponent.
"Until 2-0 we played it very stable, with confidence, with patience, with good choices and we played, I'd say, quite well.
"After the 2-0 I think everything changed and we stopped to play, stopped to think and stopped to play seriously.
"We stopped to make the right decisions on the pitch and we could put ourselves in trouble, but they didn't score and the third goal came."