Watford’s already-slim survival chances took a heavy blow when Pontus Jansson’s last-gasp winner secured victory for Brentford.
The Hornets had started the game six points from safety, but required at least something from the match only to be denied when Jansson headed home in added time to secure a 2-1 win for the Bees.
Watford’s defensive frailties were evident throughout the game, and Brentford took an early lead when Christian Norgaard slotted the ball into the net from an unmarked position in the centre of the box.
The home side had to wait for their chances, but Emmanuel Dennis struck on his return to the starting line-up to draw his side level early in the second half.
Watford have equalled a record for the longest wait for a clean sheet at home with 21 games since their last in the Premier League, a memorable 3-0 win over Liverpool in the 2019-20 season.
Ismaila Sarr had a chance to give his side the lead in the 11th minute, when he headed over from inside the six-yard box from a Kiko Femenia cross, in Watford’s only significant opportunity in the early stages.
Watford’s defensive frailties were on show again as Brentford took the lead in the 15th minute.
Ethan Pinnock’s long throw was flicked on by Kristoffer Ajer to an unmarked Norgaard who was able to tap home from six yards.
Watford struggled to string passes together and form a cohesive attacking threat while Brentford looked threatening and could have doubled their lead when Vitaly Janelt dragged the ball wide from outside the box, and just beyond the reach of Ivan Toney.
Janelt then fired wide just before the half-time break, with Watford again unable to clear the ball effectively.
The Hornets did get another chance to level when Mads Bech Sorensen almost put the ball past his own goalkeeper David Raya under little pressure from a Watford free-kick.
Brentford had an ideal opportunity to build on their advantage in the 53rd minute when Christian Eriksen clipped a free-kick over the defenders to Toney, who was in a good position, but fluffed his shot.
Against the run of play and with their first real chance of the match, Watford hit the equaliser in the 55th minute.
Moussa Sissoko’s cross was flicked on by Sarr before falling to Dennis at the far post, and he made no mistake to slot the ball past Raya.
The goal was originally ruled out for offside, but was allowed to stand after VAR reviewed and ruled that Sarr was onside when he played in Dennis.
In added time at the end of the game, Watford had the chance to take the lead only for Dennis to hit the bar and Imran Louza to scuff the final chance.
However, in the final moments of the match, Brentford retook the lead.
Eriksen played the ball across to Jansson who found the back of the net to ensure the Bees secured all three points.
