The unfortunate Troy Deeney turned the ball into his own net in the second half as Sam Allardyce’s team made it three Premier League wins in a row.
It was a tight affair, with Mamadou Sakho heading Yohan Cabaye’s corner over the bar in the opening stages while, when the Hornets responded, M'Baye Niang’s long-range shot was straight at Wayne Hennessey.
After a dull period Cabaye had a 38th-minute shot blocked after the Frenchman had been set up by the tricky Wilfried Zaha who lashed his own shot over the bar two minutes later.
On the stroke of half time Valon Behrami’s volley sailed over the crossbar to sum up a grim first 45 minutes of poor quality football.
Watford created the first opening after the break but Etienne Capoue’s effort from outside the box was too high.
Zaha fired wide after being set up by Andros Townsend but the Eagles scored the vital goal in the 69th minute when Cabaye's free-kick was turned into his own net off the near post by Deeney.
The goal seemed to settle Allardyce’s side and Christian Benteke went close to doubling their lead in the closing stages while Cabaye’s volley flew narrowly wide of the left-hand post.