The Watford boss stunned everyone at the final whistle by asking all the home fans to stay behind and boo his players as they took part in a mock penalty shoot-out competition.
It was an inspired, yet equally very obvious move by one of the smartest young managers in the game, as he sought to recreate the atmosphere and drama of a penalty competition which his side may well require in the end of season lottery.
But Watford were good value for a first win in five matches after an excellent first-half performance in which they should have been more than a goal to the good.
The Hornets nearly made the breakthrough from their first meaningful attack when an Anthony McNamee corner was headed against the underside of the bar by Ashley Young.
The rebound fell for Clarke Carlisle who connected well but saw his effort well saved by Lewis Price and then Malky Mackay struck the rebound well but saw his shot blocked.
Young curled a free-kick narrowly wide but Ipswich then came into the game with Dean Bowditch shooting wide before Ben Foster twice did well to deny Alan Lee and Nicky Forster.
However, it was no real surprise when Watford went in front just after the half hour.
Chris Eagles attacked the heart of the Ipswich defence before sliding in McNamee whose precise cross to the far post was headed into the roof of the net by Henderson.
And the visitors could have no real complaints had the Hornets scored a second before the interval which they so nearly did when Young's attempted close-range finish was deflected behind by Price.
The Tractor Boys sought to take the game to the home side after the break and they equalised when Forster got in front of the defence to head a Darren Currie free-kick firmly past Foster.
Watford thought they'd regained the lead soon after but Henderson's close-range effort was ruled out for offside.
But after surviving what looked to be a close penalty call when Mackay appeared to trip Lee, Watford got their attacking game going again and scored the decisive second when Lloyd Doyley's through ball found Young in space and his wonderful cross was crying out to be headed home which Henderson duly did.