United boss Jose Mourinho said, "It's never easy. It's always difficult here. If we score a second goal then you are in control but when they are alive, they are alive and they go until the end. They are a brave, physical team with a direct approach and pressing a lot around the box is really difficult to play against. Season after season, they are doing what they are doing.
"If you don't score you are in trouble, they go direct, they are consistent in their approach it is really difficult. We defended very well, and it is fair to say Mike Dean and his team were very good. There was a lot of first ball, second ball and the physicality."
On the winner, Mourinho added: "It was amazing but sometimes people look at strikers and analyse just the number of goals, which is not fair because he [Lukaku] is a team player and today the quality, the vision, the pass to make Martial face the one against one was fantastic."
Mourinho was delighted with Martial's overall performance.
"We know that when we can put him in the one-on-one situation with the full-back [Phil Bardsley], it's difficult for the full-back because he has so many attributes - he can go inside, he can go outside, he can shoot to the far post and he can shoot like he did today to the front post. He has lots of attributes, so it's one more reason to be happy with Romelu because Romelu knew that if we put Anthony into the one-on-one situation, it's difficult for the right-back."