In the reverse fixture at Vicarage Road in November, Louis van Gaal's strange substitution and subsequent tactical switch almost proved costly as United escaped with an injury time winner.
On Wednesday, however, it was a change of shape that proved pivotal as United improved after Anthony Martial and Marcus Rashford switched positions shortly before half-time.
Van Gaal admitted after the game that he had been on the verge of taking off Juan Mata, but gave his captain further minutes to see if he would run off a knock.
Good job you didn't Louis!
Ander Herrera was hooked instead as Jesse Lingard came on for the closing stages, but Rashford's pace and trickery from wide caused Watford problems and it was Martial whom was felled by Britos that led to the match winning free-kick late on.
Martial- on his return from injury- looked isolated and impudent when stationed on the right wing and United's attacking threat was greatly diminished as a result.
When he was pushed up top, with Rashford cutting in from the flank, the tempo of our play quickened and the young Frenchman instantly began to look quicker and sharper in his preferred and most natural position.
As the young attacking duo came to life and began to pin Watford back, United instantly upped the ante and grappled momentum away from the visitors.
Van Gaal later said that he switched the pair to "get them both into the match more".
Perhaps not 100% fit and well marshalled by an organised and disciplined Watford backline, Martial drifted in and out of the game.
But when the time came he burst into action, bringing the fans to their feet with a simply brilliant piece of individual play that proved to be just as important as the goal itself.
Marcos Rojo was solid at left-back and gave us an edge down his flank whilst Guillermo Varela stood up well to the threat posed by Watford winger Etienne Capoue.
Juan Mata was officially voted the man of the match in our 1-0 win, but I thought that Rashford was equally as impressive.
It was his quick link-up play and fleet of foot that opened up their defence and he could have scored on a couple of occasions, with one such effort flashing across the box without a touch to take it in.
Having made a crucial clearance off the line at the other end, he began posing considerable questions and then set up Memphis whom should have done better from the youngster's delivery.