United cruised to a 3-0 victory over the Black Cats at the Stadium of Light with Zlatan Ibrahimovic, Henrikh Mkhitaryan and Marcus Rashford providing the goals.
Sunderland manager David Moyes insists the controversial decision to send off Sebastian Larsson was a decisive factor in his side slipping closer to relegation from the Premier League after a 3-0 home loss to Manchester United on Sunday.
It was 35-year-old Ibrahimovic's 250th strike since he turned 30, and the evergreen Swede believes he has more than compensated for increasing physical limitations with a better understanding of his craft.
United closed to within four points of fourth-place Manchester City, on whom they retain a game in hand, but will drop back to sixth if Arsenal win at Crystal Palace on Monday. "I am not anxious, I just play my game, I try to enjoy and it seems that the older I get, the more intelligent I get".
Mourinho's overall thoughts: "We got the three points and it was a solid performance against a team which is sad - that's normal - and when you play against a team that is sad, if you score before them the game is nearly over because it's hard to react".
United play Anderlecht in Brussels on Thursday in the first leg of their Europa League quarter-final.
"I don't want to blame referees for my position and us losing", he said.
"The Europa League is the competition we can still win, so when Sergio plays in the Europa League and when we are giving him this confidence to play, it's because we know that his answer is positive and today he looked like he was really comfortable".
Bailly is one of six United players aged 24 or younger that have 10 or more league appearances this season with several other youngsters in the squad yet to play.
In the 89th minute Ibrahimovic combined with substitute Rashford who beat Pickford with a cross-shot for his first league goal since September.
But Lukaku equalised in the 23rd minute, heading in an exquisite cross by Ross Barkley, and after Phil Jagielka had headed in from a corner, Lukaku smashed in his second with over half an hour to play.
Sunderland will consider an appeal against Larsson's dismissal with Moyes convinced his midfielder was harshly treated.
"We have lots of injuries, I don't think it's even possible for us to rotate a lot", he added.