David Wagner did not understate the importance of the mission entrusted to Tom Ince when he sprang the winger from the bench just after the hour. “This is a time for miracles,” Huddersfield’s manager told the player. For 30 minutes it did not look like Ince or anyone else would find the goal the home side craved but if there is one thing that Wagner can count on from his team, it is that they will not give up. And in stoppage time Ince fulfilled his formidable task, stabbing the ball into the net from five yards to trigger mass celebrations at the John Smith’s Stadium.

“Maybe we have not the best players but for sure we are one of the best celebrators,” quipped Wagner after a victory that does a power of good to Huddersfield’s hopes of defying pre-season prophecies of doom by avoiding relegation. They are seven points above 18th-placed Southampton, albeit having played a game more. “It was a very emotional moment for everybody who supports Huddersfield. This could be one of the biggest moments in the recent club history. This moment of magic from Incey – it was a big step for sure, even if we know the job is not yet done.”

Wagner had called for a renewal of the aggression and intensity that has characterised his team’s unlikely rise over the past two years and he got it from the start. The question was whether Huddersfield could find precision to complement their tenacity. The answer for most of the match was negative, as it has often been this season for a side who had scored 26 goals in their 33 matches before this one. They worked themselves into positions to penetrate but failed to produce a cutting final ball. When they needed a scalpel they had only a plastic spoon. Their lone striker, Steve Mounié, looked hungry but was given little to feed off before being replaced in the 70th minute.

Tom Ince scores Huddersfield’s late winner. Photograph: Jan Kruger/Getty Images

Watford were worse. Theoretically Javi Gracia’s men are not out of the relegation woods themselves but they started here as if convinced they were already safe in practical terms. A ridiculous five-minute spell from Roberto Pereyra summed up most of the first half. In the 27th minute he took their first corner and hit it straight out of play. Ninety seconds later he did exactly the same thing. And soon after that he was booked for diving.

It was easy to see why Watford have not won away since November, nor scored in their last seven matches on the road. But amid the absurd sequence involving Pereyra, Watford started hinting at a threat, as Abdoulaye Doucouré burst from midfield and supplied Troy Deeney, whose shot from 16 yards was deflected wide. Doucouré sensed blood and began to break forward more regularly, one fierce low drive from the Frenchman forcing a save from Jonas Lössl. The interval came at a good time for Huddersfield.

Huddersfield curbed the visitors’ enthusiasm early in the second half but were unable to worry them. Gracia sought to give his team new impetus by introducing Richarlison for Femenía just before the hour. Will Hughes got the message and soon showed some samba skills straight out of Surrey, as the Weybridge native dribbled past three Huddersfield defenders in the box before being foiled by a fourth.

Wagner introduced Ince and Laurent Depoitre, and it was the latter who prevented Sebastian Prödl from clearing a punt into the box. Mathias Jorgensen pulled the ball back across goal, where Ince poked it into the net. A predatory effort that helps keep Huddersfield alive in the top flight.