The Blades made it three games unbeaten and five points in a week with a hard-earned point at Leyton Orient.
Against one of League One's frontrunners, 1,128 Unitedites were appreciative of the efforts of the players at the end of the game.
Conor Coady's first senior goal gave the Blades the lead but Dean Cox levelled late on for Russell Slade's side, half-volleying into the top corner.
Maguire and Baxter returned to United's starting line-up which forced a little reshuffle for manager Clough. Hill moved out to left back with White ahead of him and Baxter partnered Porter.
Just six minutes in, McMahon picked up the game's first booking for a foul on Batt and although the home side were the quickest out of the blocks, their early threats resulted from set-pieces. From a James corner on 15 minutes, Long did well to save Clarke's shot and the Blades goalkeeper gathered at the second attempt, despite having Batt laid upon him.
Another corner saw Baudry head over under pressure whilst centre half Clarke strode forward to lump a number of throw-ins into the box. From open play, on 22 minutes, Mooney linked up with Cox, but the former's shot was pulled across the box and wide.
The pace of Batt caused United major problems twice in the space of as many minutes just after the half hour mark. He outran Hill and Doyle before laying off to Cox, who was in space but Long was ideally placed to make a tremendous save, low to his right. McMahon was next to be beaten by the speed of Batt but this time Long sprinted off his line to smother.
Orient may have had the better of the first half but United were resolute and going forward there were a number of corners, whilst on the stroke of half-time, McGinn had a shot blocked and a chip from McMahon was plucked out of the air by goalkeeper Jones.
Early in the second half lashed efforts from Odubajo and Baxter failed to trouble either goalkeeper, whilst Long saved again from Mooney, even though the striker was pulled up for offside as the shot was unleashed.
Doyle accepted a booking for a foul on Vincelot, who robbed Baxter soon after but Batt was unable to take advantage. Going forward, a neat move involving McMahon and Doyle saw Baxter fire wide on 64 minutes.
The lead, however, was just moments away for the travelling fans. Baxter and White - who took a whack in the face for his troubles - battled away before Porter unselfishly laid off into the path of the advancing COADY, who calmly placed home his first Blades goal.
White was forced to leave the field with his injury, replaced by Lappin, whilst Maguire picked up United's third booking with 15 minutes remaining.
Expectedly, the home side renewed their efforts and Batt went close before the leveller arrived on 81 minutes. A loft into the box was only half-cleared and the ball dropped neatly for COX, who half-volleyed into the top corner, giving Long no chance.
Taylor replaced Porter, followed later by Baxter making way for Murphy, who quickly attempted to make his presence felt with a run at the home defence.
Six minutes of added time astonished a few inside the stadium and there were chances at both ends. Bartley had an effort blocked and a run from Murphy ended with a shot saved by Jones.
Three minutes into the extra period, from Cox's cross, Long pushed a Bartley header around a post and from the resulting corner the Blades goalkeeper held Mooney's header.
Orient: Jones, Omozusi, Vincelot (Bartley 88), Cuthbert (Simpson 72), Baudry, Cox, James (Wright 69), Mooney, Odubajo, Batt, Clarke.
Unused: Sawyer, Larkins, Lasimant, Gorman.
Blades: Long, White (Lappin 72), Maguire, Hill, Doyle, Porter (Taylor 78), Baxter (Murphy 85), McGinn, Collins, Coady, McMahon.
Unused: Howard, Miller, Cuvelier, King.