Impressive strikes from Callum McFadzean and Jordan Slew ensure that the Blades are firmly in the hunt to claim the FA Youth Cup.
In Tuesday evening's first leg encounter at Bramall Lane - which attracted a fabulous crowd just shy of 30,000 - John Pemberton's side more than matched the Premiership champions from across the Pennines.
As well as the goals from McFadzean and Slew, the visitors were forced to clear off the line twice, whilst there was a spot of controversy regarding Manchester United's first goal.
Slew, who missed the semi-final second leg against Aston Villa due to suspension, was available again and started for the Blades. Long, Harriott, Maguire and Kennedy, who like Slew, have experienced first team football this season, also started. Manchester United included Will Keane, who scored a hat-trick in their semi-final win against Chelsea, and his twin brother, Michael.
The Blades made a nervy start, conceding two corners in the opening two minutes, but the first serious chance fell to the home side. Six minutes had elapsed when Gregory came in from his position on the right and headed just over from Slew's cross.
Barry blocked Lingard's goalbound shot but the Blades were not so lucky on 14 minutes when the visitors controversially took the lead. From Pogba's delivery, goalkeeper Long challenged with LINGARD, forcing the ball to loop up and hit the crossbar and Maguire before one of the referee's assistants signalled that the ball had crossed the line. Blades fans were not convinced but the goal stood.
Buoyed by the opener, Manchester United were enjoying the majority of possession and forcing the Blades back. Maguire needed to clear off the line after Morrison's long run and shot and then Long was forced into a save from Michael Keane, arriving late from the right.
The Blades, however, continued to battle and began to give the visiting defence issues to think about. A leveller almost arrived on 33 minutes from McFadzean's corner, a header from Whitehouse looked to be heading into the net before Thorpe, positioned on the line, deflected the ball over.
The endeavours of the young home boys, though, were rewarded on the stroke of half-time. The equalising goal was made by skipper Whitehouse's enterprising run, holding off two markers, before supplying McFADZEAN, who drilled a 25-yard left-footer into the bottom corner, catching goalkeeper Johnstone cold.
Just a matter of seconds remained before the sides disappeared down the tunnel at the break with both managers, no doubt, altering their half-time team-talks.
The sides were evenly matched in the opening ten minutes of the second period with both goalkeepers forced into a save. Long held on to an effort from Van Velzen after the winger had cut in from the left and then Slew's 25-yard effort was pushed over the crossbar by Johnstone.
Manchester United were forced to clear off the line once more on 57 minutes. This time it was Fornasier who saved the visitors, kicking away Whitehouse's effort after Gregory had nodded back Slew's cross.
The entertaining start to the second period continued with another chance a minute later, this time at the other end and Long made a fine, one-handed save from Morrison after McFadzean had squandered possession. Moments later Will Keane fired just wide.
Chances and the end-to-end action continued and the visitors reclaimed the lead with 70 minutes gone. Long managed to get a touch to Lingard's cross but not enough to deflect it away from WILL KEANE, who slotted into the empty net from close range.
The Blades, though, deservedly levelled once more with the very next move. On 73 minutes, Ironside flicked on and SLEW picked his time to fire in a shot, which took a telling deflection off a defender to beat the visiting goalkeeper.
Boss Pemberton made a couple of substitutions and then was forced into a third when Maguire limped off, whilst it was the visiting side who were registering the chances late on. Tunnicliffe fired wide and then Morrison beat two but saw his shot blocked by the legs of Long.
Long made another save, from Tunnicliffe on 88 minutes, and Kennedy blocked from Cofie as the pressure intensified. In injury-time Tunnicliffe missed the target to confirm that the sides go into next Monday's second leg all square.
Sheffield United: Long, Montgomery, Barry, Harriott, Maguire (Pomares 86), Kennedy, Gregory (Wilkinson 72), Whitehouse, Ironside (Martin 74), Slew, McFadzean.
Unused: Willis, Ahmadi.
Manchester United: Johnstone, M. Keane, McGinty, Thorpe, Fornasier, Tunnicliffe, Lingard, Pogba, W. Keane, Morrison, Van Velzen (Cofie 75).
Unused: Massacci, Coll, Fryers, Lawrence.
As it Happened
Sub: Carlos Pomares on (86m) for Harry Maguire
Sub: John Cofie on (75m) for Gyliano Van Velzen
Sub: Connor Martin (74m) for Joe Ironside
GOAL: Jordan Slew (73m)
Sub: Liam Wilkinson on (72m) for Corey Gregory
Goal: Will Keane (70m)
GOAL: Callum McFadzean (45m)
Goal: Jesse Lingard (14m)
Jordan Slew is available again and starts for the Blades against Manchester United on Tuesday evening.
The striker, who made eight first team appearances for the first team this season, missed the FA Youth Cup semi-final second leg against Aston Villa due to suspension.
George Long, Matt Harriott, Harry Maguire and Terry Kennedy - all of whom have experienced first team football for the Blades this season - all start.
Manchester United include Will Keane, who scored a hat-trick in their semi-final win against Chelsea, and his twin brother, Michael.
Blades: Long, Montgomery, Barry, Harriott, Maguire, Kennedy, Gregory, Whitehouse, Ironside, Slew, McFadzean.
Subs: Pomares, Willis, Wilkinson, Martin, Ahmadi.
Manchester United: Johnstone, M. Keane, McGinty, Thorpe, Fornasier, Tunnicliffe, Lingard, Pogba, W. Keane, Morrison, Van Velzen.
Subs: Massacci, Coll, Cofie, Fryers, Lawrence.
Big Match Preview
The Blades U18s tonight play the first leg of the Club's first ever FA Youth Cup Final - and they couldn't have a higher profile challenge.
Manchester United arrive at the Lane for their 14th Final (kick-off 7.30pm), with the second leg at Old Trafford next Monday, and now the preparations are almost over coach John Pemberton anticipates that his squad is up for the occasion:
"The kids are looking forward to it, a bit nervous maybe because of the size of the crowd that will be here but that's understandable.
"I am hoping that the fact that we have played and trained at Bramall Lane before will hold us in good stead even though the attendance is likely to way above anything that most of them have experienced before as players."
The Club has pulled out all the stops in an effort to fill the stadium and with virtually all seats accounted for Pemberton's boys are guaranteed a wider audience than ever before:
"They have thoroughly deserved it after how the lads have progressed this season and it is great that they can pit themselves against a club like Manchester United."
Just how many of the Blades' group go on to carve out a career in the professional game will become clear over the next few years but they have all been made aware that the rate of progression is notoriously low - even more reason to take their opportunity tonight:
"We chatted as a group on Monday and I pointed out that for many of them it is likely that this will the biggest game they will have in their careers and they must not let it pass them by. They have to cope and go into the second leg with a bit of confidence.
"They might look big lads but many are still only 17 years old - and 15 in the head sometimes! It is a case of getting to know them, getting inside their heads and finding out what makes them tick and what doesn't
"I hope that we are a shining light for the club at the end of a difficult season. The fans at this club have always been fantastic; they will stick with us and hopefully we will be okay next season."
The two leg format for the final potentially brings further tactical considerations in to play for both teams but Pemberton is in no doubt about his intentions:
"We will try and win both games as we did against Aston Villa in the semi, not just the first and then go away and hope to hang on. If we do then there can be no argument about whether we deserve to win, and if we fall short we won't have any regrets about how we went about the job.
"I know their coach, Paul McGuiness, very well and when we played them earlier this season we drew 1-1 in an excellent game."