Brentford came out on top in a thrilling game at Vicarage Road that Watford should have won after Louza had a great chance in stoppage time.
However, the visitors went up to the other end, and Jansson scored the winner in the 95th-minute.
At the breakthrough Norgaard, the Bees led 1-0, but Dennis equalised for Watford in 55 minutes.
The hosts piled the pressure on their opponents, searching for a late winner.
But they couldn’t find one, and Brentford made it 2-1 to make it three wins on the bounce.
WATFORD (4-3-3): Ben Foster;
Kiko Femenia, Samir, Christian Kabasele, Hassane Kamara;
Imran Louza, Juraj Kucka, Moussa Sissoko;
Ismaila Sarr, Joao Pedro, Emmanuel Dennis.
BRENTFORD (4-3-3): David Raya;
Kristoffer Ajer, Ethan Pinnock, Pontus Jansson, Rico Henry;
Christian Norgaard, Vitaly Janelt, Christian Eriksen;
Yoane Wissa, Bryan Mbeumo, Ivan Toney.
Norgaard fires the visitors 1-0 ahead after 15 minutes! A long throw comes into the penalty area from the right by Pinnock, and it’s easily flicked on at the near post by Ajer, and it falls straight to the feet of Norgaard, who drills the ball home from close range.
It looked like the goal had been ruled out for offside, but VAR has taken a look at the goal and has decided that Sarr wasn’t offside as the cross came in from the right. Therefore the goal from Dennis, which was an excellent finish at the far post, is allowed to stand, and it’s 1-1!
Watford should have won it at the other end just moments earlier, but they didn’t take their chances, and Jansson punished them! It’s another superb delivery from Eriksen as he delivers a deep free-kick into the box, and Jansson meets it, powering his header past Foster to make it 2-1.
So, what’s next?
Watford remains 19th and six points from safety, with just six games left to play, and they will face Manchester City next time out. Meanwhile, Brentford moves up to 11th, and they face Tottenham next weekend.