The Hornets came into Saturday’s game eight points outside the Championship’s top six, but with a game in hand on all those above them, and knew that a win would keep them in the hunt for promotion.
Albert Riera set Beppe Sannino’s men on their way, but they were pegged back by an Anthony Wordsworth goal early in the second half.
However, the hosts did what was required thanks to two goals in three minutes from Gabriele Angella and Lewis McGugan.
Ipswich, who started the day a point outside the play-offs on goal difference, had the better of the game in terms of possession and territory in the early stages, but they were unable to create a great deal, although Manuel Almunia had to be alert to deal with shots from Daryl Murphy and Jonny Williams.
Watford’s first opportunity came on the counter-attack when Riera set Davide Faraoni away and he tried to release Mathias Ranegie, but two fine challenges from Aaron Cresswell dealt with the danger.
But the Hornets made the breakthrough in fine fashion in the 21st minute when Riera received the ball in the opposition half and drifted inside before curling a right-footed shot past Dean Gerken from the edge of the area.
Their tails up, Watford began to move the ball around more and more confidently, but they were unable to test Gerken again before the interval, although Cresswell had to deal with a dangerous McGugan cross as Ranegie waited to pounce at the back post.
After Frank Nouble and Troy Deeney had traded shots at the start of the second half, Ipswich equalised in the 50th minute when, following a throw on the right, Nouble crossed towards the near post and Wordsworth got in front of Angella to stab home from close range.
The visitors almost went in front when a Williams cross from the right was met by the head of Luke Hyam, but Almunia superbly tipped it on to the underside of the bar.
That was a close call for the home side but, soon after, they stunned their opponents with a two-goal salvo which won the game.
The first came when the Hornets were awarded a free-kick midway inside the opposition half which Daniel Tozser swept towards the far post and Angella capitalised on some poor Ipswich marking to nod down and inside Gerken’s far post.
And the hosts sealed the points when Tozser darted in between two defenders on the right side of the area and, although his cut back was blocked, it sat up perfectly for McGugan to fire across goal and into the far corner.