The Blades deservedly booked their place in the Capital One Cup semi finals with a memorable win over Premier League side Southampton.
Marc McNulty pounced on 63 minutes to secure the decisive goal while the Saints had Florin Gardos sent off late on to compound their woes.
The victory was nothing more than United deserved after being the better side throughout, producing the greater chances and showing much more endeavour and determination.
United pressed superbly from the start and punished any sense of complacency from the Premier League outfit.
Despite the starry line-up from the visitors, they found it incredibly difficult to unlock the Blades’ hard-working defence.
And United looked particularly threatening themselves on the break with Jamal Campbell-Ryce producing a couple of surging runs.
The hosts went closest in the first quarter of the game when Florent Cuvelier’s free kick drifted just over the bar.
But Southampton really should have taken the lead on 25 minutes when Mark Howard made a howler.
The Blades keeper dropped the ball from a lofted free kick but Victor Wanyama failed to punish the error as he could not stretch enough to get a foot on the loose ball.
United looked the more up for the game as the half wore on and consistently caught Southampton out with good pressing and quick movement of the ball.
Louis Reed had the crowd off their seats with a long range strike but it flew narrowly over the bar.
And the Blades were flying as half time approached.
McNulty collected a long ball over the top and crossed for Cuvelier who scuffed an effort just wide of the post.
Southampton went close on the stroke of half time when Shane Long surged into the box and cut back for Mané who struck just wide under pressure from Chris Basham.
The breathless pace of the clash continued to the second half with the Blades continuing to more than hold their own.
Jamie Murphy probably should have given United the lead just after the break when he connected with a deep cross but drilled wide of the target.
Fraser Forster had been forced into two excellent saves from a Jay McEveley header and a Michael Doyle strike.
After peppering Fraser Forster’s goal early in the second half, United finally got the breakthrough on 63 minutes.
Bob Harris drilled a free kick through the wall, Forster fumbled and McNulty darted in to score.
It was no more than United deserved after a superb performance against a side 44 places higher in the league ladder.
Mark Howard produced a fine stop with his legs to keep out Sadio Mané as Southampton began to threaten after falling behind.
But United hardly retreated into themselves to protect their lead.
Both McNulty and Murphy drew saves from the busy Forster, without whom Southampton would likely have been dead and buried.
The Saints’ night grew worse as full time approached when Gardos hauled down goal hero McNulty and was shown a second yellow card.
Blades: Howard, Harris, Basham, Flynn. Doyle, Murphy, McNulty, McEveley, Campbell-Ryce (Adams 46), Reed (Wallace 81), Cuvelier (Baxter 73).
Subs not used: Turner, McGahey, Higdon, Kennedy.
Southampton: Forster, Clyne, Fonte, Gardos, Targett (Isgrove 46), Wanyama (Alderweireld 74), Schneiderlin, Ward-Prowse, Bertrand, Mané (Mayuka 71), Long.
Subs: K. Davis, Yoshida, Reed.
Referee: Chris Foy (Lancashire)
Nigel Clough made five changes in a bid to see the Blades through to the semi finals of the Capital One Cup.
Out went Paddy McCarthy, Keiran Wallace, Jose Baxter, Michael Higdon and Chris O’Grady with Chris Basham, Jamal Campbell-Ryce, Florent Cuvelier, Marc McNulty and Louis Reed all coming in.
Ronald Koeman also made five changes from his side’s defeat at Burnley last weekend.
In came Florin Gardos, Matt Targett, Morgan Schneiderlin, James Ward-Prowse and Shane Long with Toby Alderweireld, Steve Davis, Dusan Tadic, Jake Hesketh and Graziano Pelle all dropping out.
Of the five players to miss out, only Alderweireld was handed a place on the bench.