Richarlison struck a late winner as Watford's 2-1 victory gave them a first league success at Swansea since 1983.
Luther Blissett and John Barnes were the scorers when Watford last won on Swansea soil.
But Andre Gray and the Brazilian Richarlison were the Hornets' heroes this time after substitute Tammy Abraham appeared to have given Swansea a share of the spoils.
Abraham finished from close range after 56 minutes to cancel out Gray's first Watford goal, but Richarlison brushed aside Alfie Mawson's timid challenge in the final minute to finish off the underside of the crossbar.
Swansea City 1-2 Watford
