What was a dire spectacle high on energy and commitment but woefully short of anything resembling quality looked like heading to its inevitable goalless conclusion until two minutes from time when Danny Webber returned to haunt his former club.
The ex-Manchester United striker, who moved to Bramall Lane the week before Aidy Boothroyd was appointed Hornets manager, has since spoken in glowing terms of the manager he so nearly worked with.
But when he flung himself forward to head home the winner after Richard Lee had superbly tipped Chris Morgan's header on to the underside of the crossbar, it must have felt like a dagger through the heart to the youngest manager in the top-flight.
If the defeat wasn't bad enough - leaving Watford four points adrift of safety and still with only one league win to their name - worse was to follow in injury time.
Already without key players Ben Foster and Marlon King, having lost Ashley Young to flu prior to the game and seen captain Gavin Mahon pick up a fifth yellow card of the season in the first half, Boothroyd could only watch in horror in as Chris Powell committed his second cautionable offence in almost as many minutes and was dismissed.
Quite how Boothroyd again picks up his confidence-shorn squad ahead of next week's trip to Manchester City is anyone's guess.
But the truth is a point was the very best they deserved from a contest that must have had the Premiership purists rushing to change TV channels long before Webber pounced.
Watford's biggest problem this season has been scoring goals and, on this evidence, they are even further away from solving away that key issue.
The closest they came was in the first half when a low, curling effort from Darius Henderson following a Tommy Smith corner forced a good blocking save out of Paddy Kenny.
Neil Warnock's side have hardly been prolific either, but the typically animated manager will argue their late fortune, because Webber was offside when he scored, was deserved after seeing his side hit the woodwork on two earlier occasions in the second half.
The Blades must have thought they had broken the deadlock when a cross from the lively Derek Geary was met by the head of Christian Nade but the ball bounced clear off Lee's far post with the keeper beaten.
Luck again favoured the home side when Mikele Leigertwood was allowed to wriggle into space in the right side of the area before striking a low centre which Rob Hulse again saw rebound off the upright.
It is victories against teams around the drop zone that ultimately decide whether those tipped as relegation fodder survive in the Premiership.
Sheffield United will fancy their chances of defying the critics after this, but Watford's prospects look very bleak.