Nervy and unconvincing all afternoon, Town dug deep and conjured the moments that mattered right at the death.
Terence Kongolo’s punt forward found its way to Mathias Zanka, and with Watford’s impressive rearguard erring for a split-second, the Danish defender teed up Ince, who steered the ball home, with visiting keeper Orestis Karnezis positioned out of goal.
The goal was the cue for manic scenes, with David Wanger racing fdown the touchline to join in with his players to celebrate.
The win pushed Town seven points clear of third-from-bottom Southampton, with it hard to avoid the conclusion that Ince’s strike will prove the pivotal moment in the hosts’ season.
In the process, it sealed Huddersfield second top-flight double since April 1956 and while their handsome 4-1 win in Hertfordshire was far more eye-catching, this was probably far more definitive as Town claimed just their second home win since December 9.
Town were afforded a major fillip ahead of kick-off with the news that relegation rivals Southampton had squandered a 2-0 lead against Chelsea to lose 3-2 in the top-flight’s early game, with home supporters collectively breathing again after the welcome and relieving development.
The pumped-up crowd provided some four-star fuel ahead of the game and during the early part of proceedings in a high-octane opening, with chairman Dean Hoyle, whose stirring programme notes provided further pre-match inspiration, joining in with the early clapping and singing.
Both he and David Wagner cajoled supporters to give their all, as they have done all season, to help propel the hosts onto victory, but despite strong backing, Town, despite producing some promising situations, could not get them on their feet with a goal.
The build-up play was neat and tidy at times, but the final ball lacked quality, with Town looking like a side who had failed to score in their previous two home games, despite plenty of effort and will.
For most of the first half, Watford looked every inch a side without an away goal since January 2, although in mitigation they conjured a couple of dangerous chances ahead of the break.
Captain Jonathan Hogg got a key touch to divert Abdoulaye Doucoure’s goalbound effort at the near post after he latched onto Troy Deeney’s flick following a free-kick.
Earlier, Florent Hadergjonaj also proved alert in a defensive sense to deflect a strike from Deeney, who earlier had become the first Warford player to reach the milestone of 100 Premier League appearances for the Hornets.
After a scrappy first half, the onus was on Town to regroup ahead of a huge 45 minutes in the context of their season, but it was Watford who had the better of it, with the hosts starting to look sapped by the occasion as nerves started to creep in.
Thankfully, Watford, despite several promising situations, lacked a cutting edge, with a number of feeble set-piece plays not aiding their cause.
At the other end, Town’s efforts were ponderous and lacked guile, with substitute Tom Ince and Steve Mounie’s slow reactions when well placed to fire off shots summing up a frustrating afternoon.
The perspiration was there, but not the inspiration.
Heading into the final quarter, home supporters raised the decibels again, with Town’s best moment arriving to an unlikely source in captain Hogg, with his drive from the edge of the box flying just wide.
But in a dream finale, Ince pushed the button, with Town now on the cusp of clinching safety.
Huddersfield Town: Lossl, Hadergjonaj, Zanka, Schindler, Kongolo, Hogg, Mooy, Van La Parra (Billing 77), Pritchard, Quaner (Ince 60), Mounie (Depoitre 77). Substitutes unused: Coleman, Smith, Malone, Lowe.
Watford: Karnezis; Janmatt; Prödl, Cathcart, Mariappa; Femenía (Richarlison 58), Doucouré, Capoue, Hughes (Sinclair 90), Pereyra; Deeney (Gray 81). Substitutes unused: Gomes, Britos, Kabasele, Okaka.
Referee: C Pawson (South Yorkshire).