The midfielder cut in from the left and drilled a right-foot shot which hit Chris Powell's shoulder and flew past goalkeeper Ben Foster.

It was United's first victory at home over the Hornets since March 1999 and it secured three crucial points in their bid to avoid the drop.

However, with West Ham also winning - at fellow strugglers Wigan - the result still left the Blades just three points above the relegation zone.

Having secured a priceless point at Charlton last week United manager Neil Warnock made just one switch, bringing in Christian Nade as Luton Shelton dropped to the bench.

Relegated Watford made three changes with 24-year-old midfielder Lee Williamson handed only his third Premiership appearance since a January transfer from Rotherham and defender Danny Shittu and striker Tamas Priskin were promoted from the bench.

Just five minutes into the match Watford captain Gavin Mahon was booked for a late and high challenge on Matthew Kilgallon.

United enjoyed all the early possession but lacked the composure to really make it count and it was Watford who had the first shot, although Al Bangura's 35-yard strike failed to trouble goalkeeper Paddy Kenny.

Tonge's 10th-minute foul on Williamson presented Watford with a free-kick of their own in the inside-right channel but Hameur Bouazza curled it wide.

United's first real chance came in the 15th minute when Clarke Carlisle slipped trying to deal with Chris Armstrong's long ball and Nade latched on to it and rounded Foster only for the on-loan Manchester United goalkeeper to recover and concede a corner from the striker's half-hit shot.

Carlisle was rightly booked in the 18th minute for trying to kick the ball out of Kenny's hands as he lay on the floor having fallen catching Bouazza's corner.

The incident sparked the almost obligatory shoving match between players from both sides but the Watford defender was the only one cautioned by referee Martin Atkinson.

Even greater controversy was sparked in the 34th minute when Stead was felled by Carlisle as he looked to break through. Referee Atkinson saw nothing wrong but was alerted to the obvious foul by his assistant.

However, the West Yorkshire official then compounded his error by booking Shittu instead of showing a second yellow card - and therefore a red - to Carlisle.

But the tension was lifted a minute before half-time when Tonge cut in from the left and drilled in a right-foot shot which deflected off Powell's shoulder and took the shot past goalkeeper Ben Foster.

Watford had their first shot of the second half less than two minutes after the resumption with Marlon King firing over after good work from Priskin on the right.

Keith Gillespie then responded by firing in a 20-yard strike which Foster needed two attempts to gather low to his left.

The winger was in the action again, following a left-wing corner, when he crossed and Chris Morgan's header bounced on to the roof of the net.

Stead tangled with Carlisle again - this time in the area - in the 57th minute but referee Atkinson saw nothing wrong as both players fell to the floor.

United then had the luckiest of escapes in the 65th minute when King outmuscled Morgan and lobbed Kenny only to see the ball rebound off the crossbar.

In the 76th minute the ball bounced around in the United box before it was half-cleared to Bangura just outside the area but his volley dipped over Kenny's crossbar.

Moments later Darius Henderson, a 55th-minute substitute for Priskin, caught Morgan in the face as he backed in and was cautioned.

Nerves began to fray as the match entered the last 10 minutes but Gillespie still managed to force Foster into a good save down at his near post.

And in a frantic end United held on for three vital points.