Striker Odion Ighalo condemned battling Brentford to a cruel 2-1 defeat with a stoppage-time winner for Watford.
The in-form striker Ighalo hauled Watford level and then hit a last-gasp winner to take his goal tally to 11 in his last seven outings.
Brentford kicked off flying high in fourth place but amid reports the club plan to replace manager Mark Warburton at the end of the season – even if they achieve what would be a remarkable promotion to the top flight.
Brentford’s task became all the more difficult in the 37th minute when left-back Jake Bidwell needlessly lunged in on Miguel Layun and was shown a straight red card.
Yet it was the 10 men who took the lead in the 53rd minute when Gray raced onto a long ball over the top and crashed his angled shot into the top corner.
Three minutes later Bees captain Jonathan Douglas was penalised for handball, although he claimed the ball hit his shoulder, but Button guessed correctly to smother Deeney’s weak penalty.
Yet Watford did manage an equaliser in the 68th minute when Ighalo continued his amazing goalscoring streak by heading in Juan Carlos Parades’ cross. The Hornets sensed they could grab a winner but were twice denied by more heroics from Button, who saved superbly from Deeney and Ighalo.
But Ighalo did snatch victory at the death when he volleyed in a pass from Matej Vydra to break Brentford hearts.