Neil Collins broke Morecambe hearts with an injury-time winner to dump The Shrimps out of the Capital One Cup.
The substitute rose above a static Morecambe defence to power home James Wallace’s corner two minutes into stoppage time as Sheffield United reached round two.
Both sides made a bright start with Mark Howard the first goalkeeper to be tested, the Blades stopper comfortably dealing with Shaun Beeley’s shot from the edge of the area on 11 minutes.
At the other end Marc McNulty drove at the Morecambe defence and saw a deflected shot go just wide of the post with Barry Roche at full stretch just after the quarter hour.
Former Blackpool man Chris Basham had a better chance for the visitors shortly after but could only power a header from a Stefan Scougall corner well over the crossbar when he should have done better.
The Shrimps were bright though and nearly took a spectacular lead, Lee Molyneux drilling a low free-kick from 35 yards against Howard’s left-hand post.
Connor Sammon then perhaps should have given the Blades the lead on 28 minutes but after being played through by McNulty who could only shoot tamely wide from 15 yards when he should have tested Roche.
The visitors were increasingly having more territory and nearly went in front 10 minutes before the break after a fine one-two between Kieron Freeman and McNulty, the former firing inches wide on the stretch after being found by a ball over the top.
But The Shrimps were more than playing their part in an entertaining spectacle, Jamie Devitt forcing Howard to beat away a swerving shot from 25 yards on 41 minutes as the opening half ended goalless.
Blades substitute Che Adams nearly scored with his first touch in the opening action of the second half but after getting in behind his shot was saved by the legs of Roche.
The visitors were well in the ascendancy as they raced out of the blocks after the break, Kieran Wallace the next to shoot just over from 18 yards before Sammon bended an effort wide shortly after.
The Shrimps weathered the early storm but chances were harder to come by in the second period, Andy Parrish heading over a Devitt corner and Mullin seeing an effort blocked after a fine turn.
Adams, a constant thorn in Morecambe’s side, brought another save from Roche five minutes from time before The Shrimps had a glorious chance to snatch a late lead.
Devitt and Mullin found themselves two-on-one with James McKeveley but the Irishman took the wrong option in the area and the chance was gone.
The Shrimps were made to pay with time almost up as Collins headed home to stun the Globe Arena and send the Blades into the next round.
Morecambe: Roche, Beeley (capt), Edwards, Parrish, Wilson, Fleming (Ellison 71), Goodall, Devitt, Wildig (Kenyon 57), Molyneux (Miller 79), Mullin. Subs not used: Thompson, McGowan, Ryan, Doyle.
Sheffield United: Howard, Freeman, J Wallace (Reed 90), Basham, McNulty, Scougall, Woolford (Adams 46), Sammon, McEveley (capt), K Wallace, Edgar (Collins 84). Subs not used: Sharp, Higdon, Long, McFadzean.
Referee: Stephen Martin
Attendance: 2,168 (785 away)