Ahead of kickoff, the pressure was on Manchester United to get a result and keep pressure on league leaders Manchester City. United haven't been great away from home this season so it was a huge surprise to see them go 3-0 up with just over half an hour played.
Even more surprising than the scoreline was the scorer of the first two goals. Ashley Young put United ahead with a great strike from outside the box, before doubling their lead with an inch-perfect free kick. Jose Mourinho's face said it all. Anthony Martial added to Watford's misery with a cool finish from outside the box and didn't look happy to be taken off fairly early on, which you would expect.
Marcos Rojo offered Watford a lifeline late on when making a silly challenge in the box to give away a penalty. Troy Deeney sent David de Gea the wrong way to deny the goalkeeper of another clean sheet.
Abdoulaye Doucoure then pulled another goal back for the home side with a great finish, but Jesse Lingard put any hopes of a resurgence to bed with a brilliant goal.
All in all, a hugely important three points for United.
After his deflected shot led to United's three points over Brighton at the weekend, Young put United 1-0 up on Tuesday night as his good form this season continues. His finish for the second, a free kick from a central position, was even better. Dele Alli may have to take back his comments that it's time for Young to retire.
Lingard gets plenty of stick from some fans but he proved on Tuesday night just what he's capable of. He put in a good performance and finished it off with a brilliant run and goal to ensure United left with all the points.
United were in complete control for most of the game and that is not something you can say about many of their away performances. They could have won this game 6-0 for all the good chances they managed to create.
In a match that should have seen United improve their goal difference, they were wasteful with their opportunities and allowed Watford back in to the game. Yet Matic hobbling off ahead of the weekend's away fixture against Arsenal wasn't a great sight for United fans.
Manager rating out of 10
8 -- Jose Mourinho picked the right starting team with the instructions to go for it early on, which is exactly what they did.
Player ratings (1-10; 10 = best. Players introduced after 70 minutes get no rating)
GK David de Gea, 6 -- Didn't have much of note to do all game. Went the wrong way for the penalty but made a late block when Watford were confident of completing the comeback.
DF Antonio Valencia, 6 -- Got forward well all game and was sound defensively.
DF Victor Lindelof, 8 -- Made his presence known early on to deny Richarlison the first chance of the game. He was in the right place at the right time to deny Watford repeatedly throughout the game. Lindelof has really started to come on in his last two performances.
DF Chris Smalling, 7 -- Made a great tackle to deny Deeney moments after he came on. Solid performance.
DF Marcos Rojo, 6 -- Made several great clearances with his head and some crucial tackles in the box when Watford tried to get back into the game in the second half. Made a silly foul to concede a penalty with 15 minutes left to play, which spoiled an otherwise good performance.
DF Ashley Young, 8 -- Put United 1-0 up with a great finish from just outside the box. He made it 2-0 with an expertly taken free kick which was reminiscent of his early days at United.
MF Nemanja Matic, 5 -- Lost possession in dangerous areas on a couple of occasions. Was taken off with an injury early in to the second half.
MF Paul Pogba, 7 -- Won the free kick for United's second goal after going on a good run. Should have scored from a Lingard free kick when he got in to position to claim a free header.
FW Jesse Lingard, 8 -- Assisted Young's first goal and was unlucky not to get a goal for himself, but was denied by a great save from the goalkeeper. He got in to some good positions and his movement opened Watford up. Delivered some good balls in to the box from free kicks and corners. With the pressure on United, Lingard popped up with a great solo goal to wrap up the win for United.
FW Anthony Martial, 8 -- Having had a couple of chances blocked, was totally cool when slotting home for his goal. He was really exciting to watch and was taken off early with Mourinho possibly having Arsenal in mind.
FW Romelu Lukaku, 6 -- Great play from Lukaku in the lead up to the opening goal and his first touch pass set up Martial for United's third. Went on a great run just before half-time and forced a good stop from Heurelho Gomes. He was largely poor in the second half though. A brilliant opportunity was presented to him but he dithered and his shot was eventually blocked. Pulled a shot just wide of the post a minute later.
MF Ander Herrera, 6 -- Replaced Matic. Worked hard and made several interceptions.
FW Marcus Rashford, 6 -- Replaced Martial with 25 minutes to play. Won the ball in a great position and set up Lukaku for what should have been a goal.
FW Zlatan Ibrahimovic, NR -- Replaced Lingard. His best moment was his celebration of the fourth goal just before he came on.