After winning just 1 point from a possible 6 in their last two games, Mourinho needed a win in their last game of the season- partly because of the need to build some much needed momentum ahead of their FA Cup final affair against Chelsea next week.
It was a poignant start to the match as the players and staff of both teams gave a guard of honour to United's longest serving player and captain, Michael Carrick who is set to retire from the game at the end of the season and join Mourinho's coaching staff.
It was a bright start to the game and not for one second did Watford seem unfazed by the occasion. United took the lead in the 34th minute as Juan Mata teed up Marcus Rashford after the Spaniard got on the end of a delightful ball from Carrick.
The second half started in similar fashion but both teams had to settle for half-chances as neither side could carve out any real openings.
We look at 3 things that United got right on the night:
#3 Squad rotation
Ahead of their FA Cup final showdown against Chelsea next week, Mourinho decided to rest some key players. De Gea, Nemanja Matic, Antonio Valencia, played no part in the game while Paul Pogba made a cameo appearance from the bench.
Their replacements fared well on the night with Carrick dictating the game expertly and Scott McTominay putting in another decent shift.
Their defence also held their ground despite Watford trying to pile on the pressure. Matteo Darmian, Daley Blind and Marcos Rojo played well and complemented the returning Eric Bailly very well. Romero made a couple of crucial saves in the first half but was largely untested in the second forty-five.
#2 A high tempo game
So much has been said of Mourinho's tendency to drop back and make the best out of his defenders' mistakes but certainly, they weren't going to do that against Watford at home!
It was an end-to-end game from the first visit and even after going 1-0 up, they tried to dominate the game and push for an exit. Despite the fact that they sometimes lacked the quality in the final third, the intent was there for everyone to see.
Rashford was deployed as a striker in the continued absence of Lukaku and his pace up front troubled the Watford defenders.
#1 Carrick's influence
One of the game's best ever servants, Michael Carrick enjoyed one final game in the red of Manchester as he lead his team out of that tunnel wearing the captain's armband.
Not only was the match a landmark one for the Englishman in this respect, but the fact that he continued to pull the strings so effortlessly in the middle of the park needs some serious praise.
He was the calming figure, prepared to protect his teammates and cover up for their mistakes. His exquisite ball over the top to Juan Mata led to the opening goal, completed 59 out of an attempted 69 passes and made 13 recoveries- the highest of any player.
A true gentleman of the game and one who will be dearly missed.