Huddersfield missed the chance to go top of the Championship as Troy Deeney's late penalty earned Watford a dramatic win.
Oliver Norwood's free-kick gave the hosts the lead, but Simon Grayson's men were hit by a second-half fightback.
Udinese loanee Fernando Forestieri netted his first Watford goal and Fitz Hall put the Hornets ahead.
After substitute Alan Lee levelled for Huddersfield, Deeney then kept his cool to win it with three minutes left.
The winner for Deeney came on his second appearance since being released from prison and ended Huddersfield six-game unbeaten run.
Huddersfield handed a debut to on-loan Leicester striker Jermaine Beckford and looked threatening early on, with Keith Southern's header destined for the back of the net only for Piccoli Neuton to clear off the line.
Forestieri hit a superb curling effort just wide of the far upright before he scored but it was the Terriers who broke the deadlock, and in some style too.
Almen Abdi fouled Beckford and Norwood stepped up to steer home a breathtaking free-kick from 30 yards out.
Deeney, who served three months for affray, almost curtailed their celebrations but his header cleared the bar, yet Gianfranco Zola's side drew level after 68 minutes when Forestieri's shot deflected off Clarke and crept past Alex Smithies.
Hall made it 2-1 to the visitors after he turned home substitute Mark Yeates' cross from close range and it looked like an upset was on the cards.
Lee, however, had other ideas and having replaced Beckford, equalised with a bullet header with six minutes left.
There was still time for a winner and when Marco Cassetti was fouled in the box, Deeney converted for a memorable first goal of the season.
Watford manager Gianfranco Zola: "I don't think it was our best performance but I will take it.
"On occasions we have played a lot better and not got the points. It was tough and we had the better chances but were 1-0 down.
"We didn't give up and no-one can say we didn't deserve to win."
Huddersfield manager Simon Grayson: "We were just a little lacklustre but that's only our second defeat of the season and the Championship is a learning curve for all of us.
"Expectations have increased and this is probably the first time we were favourites to win a game and that can get in people's heads."