The Tigers were by far the better team in the first half and took the lead when David Meyler headed home after a Corry Evans shot had rebounded off the crossbar.
Watford improved after the break and Almen Abdi hit the post before the Tigers doubled their lead through Robbie Brady's 25-yard free-kick.
Nathaniel Chalobah could have set up an exciting finale had his shot not been cleared off the line, although the Hornets did score in injury time when Troy Deeney netted his seventh goal in six games.
Bruce said: "Watford in the second half were better but the first half I can't really remember my goalkeeper having a touch of the ball and we've had two chances in the first three minutes which we've missed.
"But we knew Gianfranco's (Zola) team would be different in the second half, they're on a great run of form but I think we were worthy winners. We could have been and should have been out of sight."
The win continued the Tigers' upward momentum in the Championship and their manager continued: "We've tried to play, we've tried to entertain, I'm delighted that the supporters are enjoying what they're seeing.
"I've got some good players who have adapted very quickly in three or months to a different regime, a different manager, a different formation, a different style if you like but I think they're enjoying it.
"Certainly I've enjoyed working with them because they're a very, very good group and let's hope we can keep continuing."
- Sports & Recreation
- David Meyler
- Troy Deeney