Watford 1 Huddersfield Town 4: Deeney sees red as Hornets' slump continues
David Wagner's side had not scored in an away game since their win at Crystal Palace on the opening day of the season, but the Terriers found themselves two ahead inside 23 minutes at Vicarage Road.
Although there was a hint of controversy over Elias Kachunga's sixth-minute opener, Watford's dismal defending was to blame when Aaron Mooy doubled Huddersfield's tally.
Watford's third red card in three games soon made matters more difficult for the hosts - Deeney receiving his marching orders after 33 minutes for a high challenge on Collin Quaner.
Laurent Depoitre's second goal in as many matches five minutes after the restart appeared to put Huddersfield out of reach, only for Jonathan Hogg's red card to hand Watford a lifeline.
But despite Abdoulaye Doucoure's 68th-minute stunner, Watford could not complete an unlikely comeback and Mooy added his second from the penalty spot late on to cap a superb day for the visitors.
Watford's defending has left a lot to be desired in recent weeks, but Huddersfield could count themselves fortunate that Kachunga's scrappy sixth-minute opener was allowed to stand.
Poor marking allowed Depoitre to get a shot off and although Kachunga was clearly in an offside position before prodding in from point-blank range, referee Michael Oliver and his assistant failed to spot it.
59 - Elias Kachunga's goal ended Huddersfield's run of 59 consecutive shots away from home in the Premier League without scoring. Terrier. pic.twitter.com/ukGyn6fmfO
— OptaJoe (@OptaJoe) December 16, 2017
The fortunes of Huddersfield's goalscorer soon changed as he was taken off on a stretcher in the 19th minute with what appeared to be a knee injury.
Richarlison could only lash over from close range as Watford finally crafted an opening, and the hosts were swiftly punished for failing to take their chance.
There were no doubts over Huddersfield's goal this time - Watford's static defence allowing the unmarked Mooy to nudge in from Quaner's cross.
And matters soon got worse for the Hornets when captain Deeney saw red having lunged in recklessly from behind on Quaner.
3 - Watford are the first team to be given a red card in three successive Premier League matches since West Ham United in August 2015. Ill-disciplined.
— OptaJoe (@OptaJoe) December 16, 2017
Richarlison thought he had pulled one back as the interval approached, only for his neat finish to be correctly ruled out for offside.
Tom Ince and Quaner both squandered good chances to extend Huddersfield's lead following the restart, but Wagner's side did not have to wait long for a third.
After combining well with Quaner, Depoitre reacted sharply to a loose ball, the Belgian charging into the area before dispatching a powerful finish across Heurelho Gomes.
Huddersfield's numerical advantage was cancelled out just after the hour, referee Oliver deeming Hogg's tackle on Richarlison worthy of a second booking.
Roberto Pereyra's curler forced Jonas Lossl into action, but Huddersfield's goalkeeper could do nothing to prevent Doucoure's venomous half-volley finding the right-hand corner.
Watford's fight-back was short-lived though and Mooy made no mistake with a spot-kick in the 89th minute after Doucoure clumsily barged into Depoitre in the hosts' area.
A goal-line clearance from Doucoure denied rampant Huddersfield a fifth, but their fans were nevertheless able to celebrate an emphatic victory.