The Red Devils battled hard against the visitors but only claimed the winner in the second half when Ashley Young’s deflected shot found the back of the net.
Manchester United’s victory kept them in second place in the Premier League table as they bid to try and keep pace with leaders Manchester City ahead of the Citizens’ visit to Old Trafford on 10 December.
Rashford struggled to help Manchester United create many chances, and Mourinho delivered an honest assessment of the 20-year-old’s performance after the game.
Speaking at his post-match news conference, Mourinho said: “Our creation was poor.
“The three players that played with Romelu Lukaku did not get the ball, we weren’t successful on the one against one.
“Marcus [Rashford] did not have a happy match at all. So we did not have that creation and could expect some defensive problems against a good team on the counter attack.”
Manchester United will return to Premier League action on Tuesday night when they travel to Vicarage Road to take on Watford.
The Red Devils are aiming to try and win the Premier League title this season for the first time since Sir Alex Ferguson’s final campaign in charge in 2013.
Manchester United finished sixth in the table last season but won both the League Cup and Europa League under Mourinho.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news