Having set his team on a war footing with an eve-of-the-game attack on the 'compulsive liars' on the punditry couches, Jose Mourinho sent out his heavy artillery.
Manchester United were big and they got bigger with every change Mourinho made, as they dug in, determined to avoid the fate of Tottenham at Vicarage Road.
Spurs had been beaten at set-pieces having been softened up by Watford's direct style but not United.
They were up for this one, fired up by the boss and his perceived injustices and were two up at half-time, both goals from set-pieces and heavily influenced by the aerial prowess of Marouane Fellaini.
Mourinho may be accused of many things but rarely the failure to make a plan.
Romelu Lukaku scored the first and Chris Smalling the second with a fabulous flash of skill, twist and volley in a tight area.
MATCH FACTS, LIVE LEAGUE TABLE AND MATCH ZONE
Watford (4-3-3): Foster 8, Janmaat 6 (Femenia 72 5.5), Cathcart 5 (Success 88 6), Kabasele 6, Holebas 5 (Masina 84 5), Doucoure 6, Capoue 5, Hughes 5.5, Pereyra 5, Deeney 6, Gray 7.
Subs not used: Gomes, Mariappa, Sema, Chalobah.
Manager: Javi Gracia 7
Manchester United (4-3-3): De Gea 7, Valencia 6 (Bailly 92), Smalling 7, Lindelof 5, Young 7, Pogba 6.5, Fellaini 5.5, Matic 6, Lingard 5.5 (Martial 71 5), Lukaku 7, Sanchez 4 (McTominay 84).
Subs not used: Bailly, Mata, Grant, Fred, Darmian.
Manager: Jose Mourinho 7
Referee: Mike Dean 7
By Nick Callow
Andre Gray pulled one back and Watford went in search of an equaliser with United reduced to 10 men in the final seconds when Nemanja Matic tripped Will Hughes and collected his second yellow card of the game.
David de Gea sprang to his left to make a splendid late save from Chrsitian Kabasele and Mourinho's celebrated the victory.
Three points to the haul and, in his own mind at least, another point proved. His team is fighting for him.
After such an impressive start to the campaign there was no surprise to find Gracia named unchanged team for fifth Premier League game.
Watford's win against Tottenham on their previous outing hinged on aerial strength at set-pieces and Mourinho required little encouragement to send out his giants.
United were without Marcus Rashford, suspended after a red card at Burnley, and Luke Shaw, not fit enough even for the bench after his injury on England duty.
Fellaini prowled around on the toes of Smalling and Victor Lindelof, often deep enough to be mistaken for a third central defender.
Just ahead, either side of Fellaini, Nemanja Matic and Paul Pogba clocked up the miles. These five six footers worked hard to ensure they were in the air-drop zone when Watford sought to deliver cross from the full-backs.
United were sharp and a positive from the start with Shaw's replacement Ashley Young, regularly jeered on his latest return the club where his career began, effective in attack on the left as the visitors gathered momentum, kicking down the Vicarage slope.
Young's early pass to Lukaku forced Ben Foster into action. The goalkeeper smothered at Lukaku's feet and saved again from Pogba's crisp drive from the fringes of the penalty area.
David de Gea's first contribution was to deny Will Hughes from a similar distance. His second was smart reflex save to push over Troy Deeney, teed-up by Roberto Pereyra, before they were overwhelmed.
Alexis Sanchez saw a strike ruled out for offside and Foster saved again from the Chilean but the home team yielded to the pressure when Lukaku found the breakthrough, 10 minutes before the interval.
Watford failed to clear a free-kick completely after it was headed square across the goalmouth by Fellaini.
The ball found its way to Young on the left, and his cross was deflected, skipped up off the turf and evaded everyone except Lukaku who was able to make contact with his hip and divert it beyond Foster.
It was certainly scruffy, bobbling into the far post before spinning over the line, and Watford found something to argue about. Their protests were led by left-back Jose Holebas, but replays showed there was no offside offence.
The goal would stand, Lukaku's fourth of the season, and Manchester United refused to ease off. Foster was forced into two more fine saves to keep Pogba out, one either side of the second goal, scored after more chaos caused by Fellaini at a set-piece.
This time it was Young's corner swung deep towards the tall Belgian who nodded the ball towards Smalling, the centre-half who received it on his chest with Daryl Janmaat for company, swivelled and hooked a volley past the 'keeper from close range.
Mourinho scrambled from his seat to celebrate, pumping his fist. Until this point, he had preferred to stay mostly out of sight as the travelling fans sang his name.
A second goal for his team seemed significant, although Watford summoned a spirited response in the second half and found a way back into the contest when Gray pounced for his second goal of the season.
Abdoulaye Doucoure, far more influential in midfield after the interval, forged through an inside left channel and cut a low cross towards the penalty spot. Gray was first to arrive in the vacant space to and applied a firm side-footed finish which faded away from De Gea's reach.
The home crowd were revived by the prospect of another thrilling comeback. Gracia's team poured forward, taking risks at the back.
Manchester United wasted good opportunities on the break and centre-halves Kabasele and Craig Cathcart made key challenges.
This time there was no sting in the tail.