The striker got across his marker to meet Dwight McNeil's splendid cross at the near post to guide a header past Ben Foster in the 73rd minute.
The result lifted the Clarets into 11th spot in the Premier League and left the Hornets scrapping for their lives at the bottom end of the table.
Here are the player ratings...
1. Nick Pope 6
Aside from one dropped cross in the second half, the England international goalkeeper gave another good account of himself. Barely had a save to make, but his handling from crosses was as assured as ever.
2. Matt Lowton 6
The right back didn't give Tom Cleverley an inch in the first half, which led to the former Manchester United man being withdrawn at half-time. The pace of Danny Welbeck, in the second half in-particular, caused problems, but Lowton coped well.
3. Charlie Taylor 6
Defended well on the whole, limiting Ismaila Sarr and Kiko Femenia to very few openings over the course of the game. Combined well with Nick Pope to snuff out Danny Welbeck in the second half when the striker threatened to break clear.
4. James Tarkowski 8
A masterclass in defending from the centre back, who needed to be on top of his game as Watford asked questions of the Clarets after the break. Made an outstanding challenge to deny Danny Welbeck from getting a shot away inside the box.