PONTUS JANSSON made the difference on his return from injury as he netted a late winner to push Brentford into the top ten conversation.
The Bees took the lead in the first half thanks to a goal from Christian Norgaard but were pegged back after Watford's Emanuel Dennis equalised.
But Brentford would go home the happier as Jansson nodded home in the dying seconds of the match.
Jansson returned from injury to start for Brentford, with Mathias Jorgensen making way in Brentford’s only change from the Bees’ surprise victory over West Ham.
Watford manager Roy Hodgson was forced into one change from his side’s defeat to Leeds.
Cucho Hernandez was sidelined with a hamstring injury, with Emmanuel Dennis taking his place in the starting XI.
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, sending the away fans into raptures of celebrations.
Ethan Pinnock’s long throw was flicked on by Kristoffer Ajer on the way through to an unmarked Norgaard, who was able to tap home from six yards.
Brentford continued to be the better side for the rest of the first half with Watford rarely threatening.
There was a blow for Frank as Pinnock needed to come off in the 20th minute with an injury. The defender was replaced by Mads Bech Sorensen.
However, there was a big moment of concern in the 43rd minute as Ajer got a clearance all wrong and he almost ended up putting through his own net.
Fortunately, the ball dropped just wide of the post, saving the defender’s blushes.
After riding out Watford’s resurgence, the Bees went in search of a winner.
Ivan Toney almost scored a goal of the season contender in the 74th minute, but his 40-yard volley bounced just wide of the post.
Ben Forster then had to be on hand to keep Ajer's header out in the 81st minute.
Watford had the chance to take the lead in stoppage time, only for Dennis to hit the bar and Imran Louza to scuff his shot on the rebound.
And then Brentford conjured up on more chance to win the game.
The Bees re-took the lead in the final moments of the match.
Eriksen played the ball across to Jansson, who found the back of the net to ensure the Bees secured all three points.
Brentford are now 11th in the Premier League table.
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