Troy Deeney's first-half penalty was enough for Watford to beat Barnsley and move up to third in the Championship.
Referee Tim Robinson pointed to the spot when Deeney prodded the ball on to the raised arm of Tykes defender Callum Brittain and though keeper Jack Walton got a strong hand to the powerful kick he could not prevent it going in.
Watford had a second goal disallowed for offside when the recalled Andre Gray tucked away a rebound after Will Hughes hit the post from 25 yards, but the visitors looked the better side for periods without creating too much.