After a goalless first half, Watford struck twice early in the second half through Ismaila Sarr and a Troy Deeney penalty.
Nigerian forward Isaac Success was introduced late in the game, replacing Sarr.
The win was Watford’s first at home in the Premier League and their second overall this season.
Going into the game, United were unbeaten in their last six matches, while Watford were winless in their last six games.
United had the best chance of the first half in the 34th minute but Jesse Lingard dinked his effort over the top after going one-on-one with Ben Foster.
But five minutes into the second half Watford went 1-0 up as David De Gea fumbled Ismaila Sarr’s strike.
And in the 54th minute Deeney converted from the spot to double the Hornets’ lead after Aaron Wan-Bissaka brought down Sarr in the box.
United are in eight position on 25 points
And Watford remain bottom on 12 points in the league table.
11 BUSINESS NUGGETS FROM SUPER EAGLES BRONZE MEDAL TRIUMPH. The content of this ebook will propel you above your competition. DOWNLOAD NOW!!!