Burnley strike partners Chris Wood and Ashley Barnes both scored second-half goals to secure three points at Vicarage Road and leave Watford at the bottom of the table.
In torrential rain, the Clarets soaked up all the pressure the Hornets had to offer before pouncing early in the second half when Wood hooked home a loose ball from a corner.
Barnes scored from the penalty spot with eight minutes left after VAR deemed Jose Holebas had fouled the Burnley forward.
James Tarkowski put the gloss on Burnley's victory late on, forcing home a rebound after his first effort had been well saved by Ben Foster.
Watford are yet to win at home in the Premier League this season and their lack of confidence in front of goal was summed up by another toothless display.
Sean Dyche's team have been equally poor on the road and showed limited ambition to contain their hosts for most of the 90 minutes.
However, in Wood and Barnes they have strikers on top form to make the difference in tight games, and this win pushes them up to sixth in a congested Premier League table.
This defeat leaves Watford mired in relegation trouble after 11 successive home games without a win for the first time in their history.