Neither side were able to get out of gear for much of the first half, with goalmouth action at a premium, though the Terriers very much dictated the pace of the game against a shy Hornets outfit.
A cautious first half eventually drew to a close without a goal being scored, and the first significant action after the restart was a collision between Will Hughes and Hadergjonaj that left the latter requiring treatment on the pitch.
Indeed, the first concrete effort did not come until the 82nd minute, Jonathan Hogg latching on to a loose ball on the edge of the penalty and slicing just wide of target.
Just as it seemed like the game would end up as a stalemate, the hosts launched a counter-attack and Mathias Jorgensen pulled the ball back for Tom Ince, who smashed home from close range to send the home crowd into a frenzy.
HUDDERSFIELD TOWN (4-2-3-1): Lossl; Hadergjonaj, Jorgensen, Schindler, Kongolo; Hogg, Mooy; Quaner (Ince 61'), Pritchard, Van La Parra (Billing 77'); Mounie (Depoitre 71')
WATFORD (4-2-3-1): Karnezis; Janmaat, Prodl, Cathcart, Mariappa; Capoue, Doucoure; Femenia (Richarlison 58'), Hughes (Sinclair 90'), Pereyra; Deeney (Gray 81')