Odion Ighalo’s early goal gave Watford their third successive win and left Sunderland stuck in the bottom three.
Ighalo and Black Cats defender Sebastian Coates met Allan Nyom’s low cross at the near post and diverted the ball past Costel Pantilimon.
Sunderland took time to find a response but dominated the second half.
Jermain Defoe and Jack Rodwell forced good saves from Heurelho Gomes but the Hornets hung on for a victory that moves them up to seventh in the table.
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