It was a game that could have gone either way, but Juan Mata showed his class as he dragged Manchester United from the ashes to give them all three points as wasteful Watford allowed them to keep another home clean sheet.
Nothing to separate in a tense opening 45 minutes
Like many teams visiting Old Trafford this season, Watford were ready to take the game to United and were very much in the match for the majority of the first half.
After a couple of dangerous crosses for both teams, Morgan Schneiderlin created the first opportunity of the game when he volleyed just wide after the visitors could not clear Mata's free-kick. Watford came back with menace as Troy Deeney flicked on an Etienne Capoue cross, before Odion Ighalo used his strength to turn but could only shoot wide.
Both teams continued to play with intent but lacked any real quality in the final third as Anthony Martial and Almen Abdi exchanged tame efforts, straight at Heurelho Gomes and over the crossbar respectively.
As the first half filtered out, Ighalo, who was guilty of missing a handful of opportunities at the weekend against Bournemouth, had possibly the best opening of the half, but he fired straight at David de Gea when teammate Deeney was arguably better placed.
Watford also had time to fashion a penalty appeal when Daley Blind flicked out a leg at Capoue, but Mike Jones waved the appeals away. A frustrating end to another first half at Old Trafford for the home fans, with United failing to register a goal and barely a shot on target.
An end to end second half sees Mata steal the headlines
Watford were beginning to sense fear in the ranks of the home side and became ever more ambitious at the beginning of the second half.
Capoue smashed an effort just over, before Sebastian Prodl had a header cleared off the line by young Marcus Rashford from a corner - the United youngster proving that he is not all about scoring goals.
Ighalo had a third chance of the game just moments later when he curled an effort wide after beating Tim Fosu-Mensah, but should have at least hit the target.
The hosts could only improve and Rashford was the man who was trying to drag them along. The youngster forced Gomes to come out and challenge him, before Mata tested the Brazilian from range. Rashford then hit a cross just inches away from his teammates and Gomes was forced into another save from Mata.
A flurry of changes disrupted the flow of the game but it almost worked in the favour of the away side. Substitute Nordin Amrabat took too long in front of goal and Blind made a crucial block, before Prodl missed a golden opportunity from the resulting corner.
Quique Sanchez Flores will only be too aware of the importance of taking your chances in the Premier League and his side were made to pay with just eight minutes left to play. Miguel Britos brought down Martial just outside the box and Mata stepped up to curl the resulting free-kick into the back of the net, sending a previously quiet Old Trafford crowd into delirium.
The Hornets were left shell-shocked and could not muster an attempt to draw themselves level as United held out to go level on points with Manchester City.