Solskjaer has made a policy of rotating his side and it was no surprise to see him ring the changes, with nine alterations in total. He handed a well-earned rest to Bruno Fernandes, who was part of a strong bench which also included Martial and Rashford.
Daniel James had started really brightly, and another promising run in from the left resulted in him getting a powerful shot off. It may have been rising over the bar, but Watford's goalkeeper took no chances as he tipped it over.
And with just six minutes gone, the Ole Gunnar Solskjaer's side had the lead. Scott McTominay met Alex Telles' outswinging corner with a brilliant header which diverted up off the turf before spinning in off the right-hand upright.
With 20 minutes gone, Telles put a brilliant cross into the box from the left flank from the corner. Eric Bailly ran away from his man and had a free header at goal, but he planted his attempt wide of the right post.
In the 35th minute, United cleared the danger, but Watford recycled possession and Ismaila Sarr sent a cross into the box. It was cleared as far as Nathan Chalobah, who drilled his right-footed strike from the D just wide of the target.
Eight minutes later, Donny van de Beek rolled a sublime backheel into the path of Juan Mata in the left inside channel, leaving the Spaniard with only Bachmann to beat but the Watford keeper spread himself and made a fine stop with his body.
The Red Devils suffered a blow on the stroke of half-time when Bailly was forced off with injury and replaced by Harry Maguire.
The first attempt of the second half came from the Hornets. Navarro and Sarr combined down the right flank, allowing the latter to whip a cross towards the back post. Joao Pedro met it, but could only steer a tame header straight at Henderson.
With 15 minutes to go, Sema worked the ball back to Navarro to whip a cross towards the near post. Gray got ahead of his man, but nodded his effort wide of the target.
Hungbo was then played into space on the right flank and he cut back to shoot on his left foot. Maguire had to get across to deflect his effort wide of the target as United saw out the win in the end.