The Anglo-Nigerian was introduced as a sesecond-half substitute and went on to impress 10 minutes later with a goal for the hosts.
Andre Gray broke the deadlock for Marco Silva’s men 13 minutes into the ecounter with a powerful shot inside the penalty area as Watford maintained their lead into the interval.
Abraham replaced Mike van der Hoorn immediately after the restart and converted a rebound after Gomes tried to save Wilfried Bony’s shot in the 56th minute.
Richarlison’s 90th minute strike condemned Paul Clement’s side to their third defeat in the Premier League this season.
Swansea City will visit West Ham United for their next league encounter while Watford make a trip to the Hawthorns to play West Bromwich Albion.