The Hornets are still seven points adrift of safety but, if they can win their game in hand, the great escape may just be on for Aidy Boothroyd's battlers.
There was certainly no shortage of spirit and commitment against Mark Hughes' side, that came into the game having scored ten goals in their previous three away outings, but for once Watford got the breaks as well.
Brett Emerton's own goal gave the home side the breakthrough they needed and, after they had been pegged back by Benni McCarthy's leveller on the stroke of half-time, Jay DeMerit made the most of a decent spell of pressure following a second-half free-kick to score the decisive second.
But do not be surprised after this victory if a petition starts at Vicarage Road to have Dermot Gallagher in charge for every one of the Hornets' remaining games this season, because he was also the referee who oversaw their only previous victory, against Middlesbrough, 12 league matches ago.
After David Bentley had fired the game's first decent opening wide, Watford began to take charge and took the lead with a slice of good fortune that has eluded them for so much of the season.
Adrian Mariappa found Tommy Smith in the inside-right channel, and the Hornets winger did well to reach the by-line, before standing up a cross that was slightly deflected en route to the far post.
Emerton had to challenge Damien Francis and duly got up above his opponent but only succeeded in heading down inside Brad Friedel's right-hand post.
Hameur Bouazza and Damien Francis, either side of a good opportunity for McCarthy, both had good chances to extend Watford's advantage before the interval, but the home side paid the price for switching off on the stroke of half-time.
Bentley latched on to a throw from the right and easily by-passed a couple of half-hearted challenges before sending over a cross which McCarthy superbly dispatched over Ben Foster with a looping header that went in off the underside of the bar.
Boosted by getting back on terms, Blackburn upped their game after the break but Morten Gamst Perdersen failed on three occasions to test Foster with free-kicks from around the 25-yard mark and Shabani Nonda also blazed horribly over.
Rovers also suffered a blow when Robbie Savage was stretchered off following a clash with Al Bangura, but the visitors were made to pay for their profligacy after 70 minutes.
Jordan Stewart whipped in a free-kick from the right, Will Hoskins got the near post flick but the stretching Malky Mackay was unable to direct his header on goal.
However, Bouazza read the situation superbly and raced in behind the centre-half to turn the ball back across the six-yard box for DeMerit to flick it wide of Friedel and inside the far post.
Watford should then have made the game safe when Stewart missed an excellent opportunity to present Hoskins with his first Watford goal on a plate, but pulled the cross slightly behind his team-mate.
That miss was almost punished when in-form Rovers substitute Matt Derbyshire headed a glorious chance over following a Bentley cross.