Sunderland continued their fine form in the Championship as they inflicted a third straight defeat on Watford, a day after boss Valerien Ismael signed a contract extension.
Niall Huggins blasted into the top corner after an excellent run to put the hosts ahead shortly before the break with the first clear-cut chance of the game.
Danny Ballard headed over after an hour for Sunderland, but two minutes later Abdoullah Ba nodded in from close range.
It should have been 3-0 when Adil Aouchiche broke through on goal, but his effort was half-saved by Daniel Bachmann before Ryan Porteous cleared the weakened effort off the line.