Midfielder Daniel Pudil plundered the winner as he was first to react when Huddersfield keeper Alex Smithies spilled Lewis McGugan’s free-kick on 44 minutes.
Fernando Forestieri was fouled by Adam Hammill about 25 yards out, with Pudil lifting the rebound over Smithies from close range to secure a 2-1 win.
Argentina-born Italian Forestieri, who scored his first goal for Watford in a 3-2 win at Huddersfield last season, earlier struck a beauty.
Watford had fallen behind on 17 minutes when Hammill crossed and Danny Ward glanced a header in unmarked after a run from deep but the Hornets were level inside a minute when Forestieri produced a lovely curling drive to cap a flowing move.
Troy Deeney played in David Faroni down the right and the former Inter Milan star squared for Forestieri to finish from the edge of the box.
Huddersfield, unbeaten at home before this match, started well and went close early on when Oliver Norwood twice blazed over.
Smithies made amends for his mistake with a good save on 30 minutes to deny Sean Murray after good play from Forestieri and Deeney.
He also parried McGugan’s shot in first-half stoppage time, with Anthony Gerrard clearing before Deeney could pounce.
At the other end James Vaughan, Town’s 11-goal top scorer, powered a header just wide from another Hammill cross driven in from the right on 32 minutes.
Former Boca Juniors and Genoa star Forestieri nearly created a third goal for Watford early in the second half with a clever through-ball.
McGugan left Gerrard trailing and fired just wide from the edge of the box as Peter Clarke and Joel Lynch closed the gap.
Gerrard’s poor ball control allowed Deeney in on 62 minutes but the defender’s blushes were spared when the striker, making his 200th senior start, blazed over.
Livewire Forestieri produced a mazy run three minutes later. Tackled by Clarke, he regained possession and saw his attempted chip over Smithies drop wide.
Watford, who dominated the second half after an even opening period, next went close with a sweeping breakaway move from a Huddersfield corner.
Forestieri, Lloyd Doyley and Josh McEachran were all involved, with the on-loan Chelsea star dragging his shot wide from Doyley’s return pass.
Huddersfield’s best chances of the second half came in a late spell of pressure. Ward curled a free kick wide from 20 yards after McGugan fouled Hammill.
Vaughan headed over from a Ward cross and the striker was denied in stoppage time when keeper Manuel Almunia saved at his feet from substitute Sean Scannell’s cross.