An Andros Townsend penalty may have given Tottenham a narrow first leg win but the Blades will feel they are far from out of their Capital One Cup tie.
United emerged from their trip to White Hart Lane with plenty of credit after another remarkably resolute defensive show peppered with moments of real threat against a side 45 places higher in the league pyramid.
The only blot on their night came after a moment of madness from Jay McEveley 14 minutes from time when he inexplicably handled under pressure from Roberto Soldado.
Townsend made no mistake from the spot but those with a Tottenham interest will undoubtedly be unconvinced that they have done enough to secure passage into the final.
United started with real intent as they looked to produce another giant killing act in the Capital One Cup.
The Blades whose late arrival at White Hart Lane forced a 15 minute delay to kick-off - pressed hard into opposition territory during the opening five minutes, forcing Spurs onto the back foot.
Jamal Campbell-Ryce and Stefan Scougal both went close to giving United the lead during the opening 45 minutes.
But the only shot on target came from the hosts with defender Eric Dier denied with a comfortable save from Mark Howard.
And opportunities arose to breach the Premier League outfit’s back line with both Campbell-Ryce and Marc McNulty darting into the area.
McNulty had the Blades’ first shot of the night but scuffed an effort from the edge of the area horribly high and wide.
Campbell-Ryce went close to giving the Blades a shock lead at White Hart Lane after a superb start to the game.
The flying winger - who had given hosts Spurs plenty of headaches in the opening quarter of the game - surged to the corner of the box and drilled across goal.
There was a nervy moment for United on eight minutes when a Spurs corner fell to on-form striker Harry Kane eight yards out but a slip allowed Jay McEveley to clear.
Striker Emmanuel Adebayor found himself the centre of controversy after 17 minutes. He swung out an arm and caught Louis Reed in the face but despite Blades protests, referee Neil Swarbrick only showed the yellow card.
Tottenham had the first effort on target on 23 minutes. Andros Townsend swung in a free kick from the right with Eric Dier rising to turn a header on target but Mark Howard saved comfortably.
There was real danger when Adebayor brought down Cristian Eriksen’s ball over the top but drilled well over the bar under pressure.
Stefan Scougall flashed a superb shot narrowly wide as United continued to threat against top flight Spurs.
The Blades caught Spurs in possession 25 yards out with the ball fed quickly to Scougall who turned and drilled a shot that drifted away from the top corner.
On the stroke of half time, Townsend and Dier combined once again from a free kick with the big centre half flicking a header just wide of the far post.
United had continued to defend with real composure and heart against an increasing Tottenham threat in the second half.
They met threat with the same resolute defending they produced in the first half, denying their hosts a real sight of goal.
Chances of real note were few and far between for much of the second half.
But then came the night’s decisive moment.
McEveley conceded the penalty on 73 minutes after sticking out his arm in his attempt to control a flick from substitute Soldado.
And Townsend smashed in his spot kick to deliver a hammerblow to the plucky Blades.
United responded well to going behind and piled on the pressure in the last few minutes.
But they failed to test Michel Vorm and head back to Bramall Lane next week with a deficit to overturn.
Tottenham: Vorm, Walker, Dier, Vertonghen, Davies, Townsend, Mason (Dembele 64), Stambouli (Paulinho 75), Eriksen, Adebayor (Soldado 64), Kane.
Subs not used: Friedel, Kaboul, Rose, Lennon
Blades: Howard, Flynn, Basham, McEveley, Harris, Campbell-Ryce, Scougall (Wallace 87), Reed, Doyle, Murphy, McNulty (Baxter 83)
Subs not used: Turner, Alcock, Higdon, Kennedy, Adams.
Referee: Neil Swarbrick (Lancashire)
Cards: Adebayor 17 (Tottenham), McEveley 54 (United)
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