Tonge unleashed a shot just before half-time which bounced on the head of Watford defender Chris Powell's head before looping over Ben Foster and into the Hornets net. The goal was officially given as a Powell own goal - but it's doubtful he will want to claim it.
It was an enjoyers day for the Blades, although West Ham United claimed a 3-0 win at Wigan Athletic to unease United's survival challenge the draw claimed at Charlton Athletic didn't go in vain as the Addicks lost 4-1 at Blackburn Rovers.
The results leave the Cutlers in 15th position and a healthy three points clear of the drop zone, the Blades now need just two more point to be playing Premier League football next season. Two defeats from their remaining fixtures against Aston Villa (a) and Wigan Athletic (h) could possibly spell curtains for the Bramall Lane club.
Sheffield United boss Neil Warnock warned fans before the game that this wasn't going to be a classic and he was right, it was a dull match but United got the points they needed.
The Blades looked anxious throughout - the desire to win three points and the Hornets bullish tactics didn't help matters
Watford have got nothing to play for except pride since they were ejected from the Premier League last weekend with a 1-1 home draw with Manchester City, but they came to Bramall Lane with some fighting spirit.
It took 15 minutes for the home side to carve out their first opportunity of the match; Derek Geary found the feet of Christian Nade who rounded goalkeeper Ben Foster but the loanee from Manchester United managed to scrambled back to force a corner.
Hornets Clarke Carlisle should have received his second yellow card of the game when he elbowed Jonathan Stead when challenging for a header. Fortunately for the former Leeds United defender referee Mr. Atkinson blundered and wrongfully booked Danny Shittu instead.
And, with two minutes remaining of the first half United took the lead through Michael Tonge. He picked up the ba;ll on the edge of the area and unleashed an almighty shot which cannoned off the head of Powell and deflected over keeper Ben Foster, 1-0.
United found their dominance in the second half an almost doubled their lead when captain Chris Morgan headed narrowly wide from a Keith Gillespie cross whilst Nade shot over the bar from a difficult angle after Foster dropped.
Watford offered some signs of snatching a point when Marlon King muscled past two challenges before looping the ball over Kenny which thankfully bounced back off the bar.