John Egan scored a 95th-minute equaliser to salvage an FA Cup fourth-round replay with Wrexham after a thrilling 3-3 draw at the Racecourse Ground
With co-owner and Hollywood actor Ryan Reynolds in attendance, the National League side fell behind inside 120 seconds when Oli McBurnie headed in a corner, but grew in confidence and deservedly levelled when James Jones bundled the ball in after Ben Tozer's long throw was not dealt with
Thomas O'Connor completed the comeback when he steered home just after the hour, but Oliver Norwood tucked home an equaliser minutes later (65) after his first attempt was repelled
Daniel Jebbison was shown a red card midway through the second half for appearing to kick out at Tozer in an off-the-ball incident on the halfway line
Wrexham's talisman Paul Mullin - who has now scored in every round his side have played in this season - thought he had had the final say, firing in after exchange passes with Sam Dalby to fire the Red Dragons ahead for the second time with four minutes to go
But Blades defender Egan stepped in to save the Championship side's blushes with seconds remaining, when he poked in at the far post to take the tie to a replay at Bramall Lane next month
With Reynolds in attendance, all the pre-match talk centred around whether Wrexham could write a script fit for the silver screen
 Within 10 minutes there had been more twists than the actor himself could have dreamed up
McBurnie headed in Tommy Doyle's corner at the near post to give the Blades the advantage in the tie, which, on paper, at least, only grew larger when central defenders Jordan Tunnicliffe and Aaron Hayden limped off injured to compound a disjointed start
But there was to be no lack of endeavour from the hosts, who dug in and felt aggrieved not to have been awarded a penalty when Mullin went to ground after chasing down a long ball, claiming goalkeeper Adam Davies had caught him, though replays suggested there was little contact
Wrexham ended the first half in the ascendancy, too, with Mullin testing Davies from a tight angle after bringing Mark Howard's goal-kick under his control and then blasting a free-kick into the wall from just inches outside the box after he had been brought down by Egan
Their fearlessness continued into the second half and finally produced a reward when one of Tozer's signature long throws was bundled into the net by Jones, before O'Connor fired in under pressure after an attempted clearance by substitute Billy Sharp to turn the tide
The drama continued when Norwood equalised after a late dash into the box to take over from Jebbison, who was, incidentally, sent off with just under 20 minutes to play after an off-the-ball incident with Tozer, that referee Dean Whitestone was alerted to by fourth official Scott Oldham
Wrexham should then have been awarded a penalty when Anel Ahmedhodzic handled a cross, but play continued, with Ollie Palmer crashing a shot off the woodwork
They got justice, however, when Mullin made a direct run into the box, collected Dalby's return pass and slotted home, but a safe passage to the next round for the first time since 1996/97 was put on hold when Egan pounced in the dying embers
"With the start we had, conceding a goal and losing two players, for the team to reset themselves as well as they did, I thought was outstanding
 A lesser group of players could have got beaten four or five nil there
 We had to re-jig the team, having lost two key players to injury, and the way we regained our composure was absolutely outstanding
"We got to half-time and I believed that we would get back in the game, I really did
 We took the game to Sheffield United, we pinned them in for long periods and it's a real blow that we haven't got over the line, so it is mixed emotions, as you can imagine
"The way the lads have performed today on the big stage was outstanding
 Character, heart, quality as well and I think that was the key thing
 We had the threat from set plays, but some of the composure we showed in possession against a really, really good team I thought was excellent
"All of those qualities mixed together are going to take this club a very long way and I'm immensely proud of what we've seen out there, but equally, there is that disappointment that we haven't got over the line
"Sheffield United manager Paul Heckingbottom praised his players for the way they handled the game
"It doesn't surprise me that we fought and dug in to keep ourselves in the hat and upset everyone," he added
"We all know why everyone turned up today and I'm glad we didn't give them what they wanted
"On Jebbison's "massively disappointing" red card, after referee Dean Whitestone took advice from fourth official Scott Oldham, the Blades boss said he had yet to see convincing evidence to warrant a sending-off and a three-match ban
"I was stood next to the fourth official and he said he'd seen something I've not," he said
"I've looked at footage and I can't see anything in it yet
 We can't just accept it, we have to get to the bottom of it
"Either Jebbo has to learn from it or if there's nothing in it we want the player and we will have to appeal it so we need some footage
"return to National League action on Saturday with a trip to  - kick-off 5
20pm - before hosting on Tuesday February 7; kick-off 7
45pm
next game is at Yorkshire rivals on Saturday, live on ; kick-off 12
30pm
The promotion hopefuls then host on Saturday February 11; kick-off 3pm
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