United slipped to a first defeat of the season, despite going toe-to-toe with 2016 Premier League champions Leicester City at Bramall Lane.
Harvey Barnes settled the contest in favour of the Foxes, despite Oli McBurnie's first for the Blades cancelling Jamie Vardy's first-half opener.
Boss Wilder made one enforced change for the clash against the Foxes, with Luke Freeman replacing the injured Fleck. Morrison was named in the matchday 18 for the first time since his summer arrival.
The Blades once again received a inspiring reception as the players emerged from the tunnel at a sun soaked Bramall Lane and that was followed by a passionate rendition of Greasy Chip Butty. On the field, the home side were quickly on the front foot, with Freeman forcing an early corner which caused panic in the Foxes box. At the other end, Tielemans dragged an effort wide after Perez broke down the right.
Gradually the visitors were getting into the game and after Fuchs had fired a free-kick wide, Vardy failed to connect properly with a header in front of the Kop. In possession though, United continued to offer a threat and Lundstram fired over from distance after some neat build-up play, with Freeman continuing to impress.
With the half hour approaching, the Blades fashioned the best chance of the game, Stevens and O'Connell combined on the left, before the latter crossed deep to Baldock, who stung the palms of Schmeichel with a dipping volley.
In the 38th minute though, it was the visitors who took the lead. Basham lost possession in his own half and after Maddison played a ball through the Blades defence, VARDY latched on to it and fired left-footed past Henderson. United looked for a response, but Robinson was adjudged to have fouled a retreating Evans from McGoldrick's flick-on. Right on the stroke of half-time, United won a corner, but from Norwood's deep delivery, O'Connell headed over from a promising position.
Early in the second-half, City almost caught United on the break, with a swift counter attack, but Egan cleared a Perez shot after he, Maddison and Vardy had combined. The Blades responded with a double change up top, with McBurnie and Robinson replaced with McBurnie and Sharp, who received a rousing reception.
Lundstram was the first player to be carded for a foul on Maddison. But the decibel level inside S2 hit a new level on 62 minutes as MCBURNIE powered home a header past Schmeichel in front of the Kop after Norwood had kept his composure to free Baldock, who provided the assist from the right.
Eight minutes later though, the game swung back in favour of Leicester, as BARNES rifled home an unstoppable half volley from the edge of the penalty area, giving Henderson no chance. The Blades refused to lie down though and only a fantastic save from Schmeichel denied Lundstram from Sharp's header down, but the assistant referee had already flagged for offside.
Basham was withdrawn and Morrison introduced for a home debut with 13 minutes left, as Wilder used his final change. The clocking was against the Blades, but the hosts kept pushing forward chasing an equaliser and forced a trio of corners in quick succession.
Four minutes of added time were signaled, which gave the Blades hope, but despite throwing everything at City, the visitors held on.
Blades: Henderson, Baldock, Stevens, O'Connell, Basham (Morrison 77) Lundstram, L. Freeman, Robinson (Sharp 54), Egan, Norwood, McGoldrick (McBurnie 54)
Unused: Morrison, Jagielka, Osborn, Moore, Bešić.
Leicester: Schmeichel, Ricardo, Evans, Soyuncu, Fuchs, Choudhury, Tielemans (Mendy 89), Praet (Barnes 62), Maddison, Ayoze (Morgan 77), Vardy.
Unused: Ward, Justin, Morgan, Gray, Albrighton, Mendy.
As it happened...
We are underway.
United in red and white and Leicester in blue.
United start with a nice spell of early possession but it is Leicester who have the first shot.
Dennis Praet takes aim from distance but his effort is blocked by his own man. 0-0.
First cross into the Leicester danger area arrives from the United left.
Enda Stevens, advanced as always, with the cross. The visitors deal with the first delivery, lively start. 0-0.
Freeman wins a corner, the volume increases...
Norwood's delivery goes right across goal and hits Robinson square in the chest before Leicester are quickest to the second ball and clear. 0-0.
Youri Tielemens with a shot from distance which he drags well wide. 0-0.
Maddison is upended by Lundstram a full 30 yards from goal.
It is a long way out but Fuchs fancies a shot here, he drills his effort a yard wide of Henderson's left-hand post.
Tielemans with a cross from the angle finds the forehead of Maddison who glances his header wide of the far stick. 0-0.
Another half chance for Leicester.
Tielemans again pulling into this wide right position to deliver a cross which is flicked well wide by Jamie Vardy. 0-0.
A slight lull in proceedings is ended as United have our first shot in anger.
Last weekend's goal hero John Lundstram takes aim from distance but fires over from around 25 yards, 0-0.
Good min-spell for United as Freeman breaks into the area but his cut back is cleared.
Just before the attack John Egan makes a classy interception as Leicester looked to get Vardy in behind.
Great to see Dave Bassett back at the Lane, sat alongside England boss Gareth Southgate.
First shot on target for the Blades.
Cross from the left by-line finds George Baldock lurking on the edge of the area.
He hits it first time, and it is a good connection, but straight at Schmeichel when either side would have been a goal.
A Leicester free-kick is drilled harmlessly into the Blades' wall. 0-0.
Goal for Leicester.
Vardy finishes well after United surrender possesion inside their own half.
Good response from the Blades.
Stevens with a dangerous centre which is put behind by Çaglar Söyüncü.
The resulting corner has Schmeichel back-pedalling but there's no touch and the ball goes through for a goal kick. 0-1.
McGoldrick flicks on a long kick by Henderson and Robinson latches onto it.
Unfortunately he fouls his man in the process and the ref blows for a free-kick with Robinson through on goal.
One minute added
Blades 0-1 Leicester
Vardy's goal seperates the sides at the break.
Blades back out here for the second half...
Robinson gets the second half underway...
Quiet start to the second half but the Lane comes alive as Stevens embarks on a weaving run.
The Irishman works his way into a good position but his pass goes astray and the move breaks down.
Egan with a crucial block as Maddison looked to shoot. 0-1.
Perez with an effort from a narrow angle, not sure if it was going in, but Egan was there to clear away from the goal line.
Attendance: 30,079 (2,865).
Double change here for United.
Wilder makes the first move by bringing on Oli McBurnie and Billy Sharp for David McGoldrick and Callum Robinson.
Lundstram into the book for a late lunge on Maddison.
Some crunching tackles going in here, but all fair. Sharp gets the Lane on its feet with one earlier and since then the atmosphere has gone up a notch.
The record signing heads in his first goal, and survives a VAR review
The ex-Swansea ace heads in Baldock's pinpoint cross from the right. 1-1. Game on!
Barnes replaces Praet for Leicester as Brendan Rodgers makes his first change.
Almost another for the Blades.
This time it is the turn of Freeman to deliver an inswinger towards McBurnie but Schmeichel punches clear.
The game is wide open now, as Egan makes a good challenge to deny Vardy following a long period of pressure from United.
Against the run of play Barnes blasts in a second for Leicester after United clear a cross to him just inside the area. 1-2.
Wonderful save by Schmeichel.
A deep cross is headed back into the mix by Sharp and Lundstram on the run fires it towards goal first time. The Dane claws the ball away with a brilliant stop, but there's also a flag for offside in the build up so it would not have counted.
Change here for Leicester as Perez is replaced by Wes Morgan.
Change for United as well as Basham is replaced by Ravel Morrison who makes his debut for the Blades.
United having all the possession now as Leicester decide to sit in.
It is patient stuff from the Blades who go in search of another equaliser.
Blades win a corner attacking the Kop End, in it goes by Freeman, Morgan heads away...
Another corner for United...
It is deep from Freeman, headed into a dangerous area by Egan towards McBurnie but Leicester scramble clear.
Final sub for Leicester as Tielemans is replaced by Nampalys Mendy.
4 added minutes
Free-kick to Blades as Freeman is felled 25 yards out...
Norwood's effort takes a deflection off the wall, corner...
Leicester hanging on as they clear twice...
Blades 1-2 Leicester
Goals from Vardy and Barnes win it for the visitors, United had equalised through McBurnie.
Great effort from the Blades who were excellent, especially second half.
Thanks for your support, we'll see you at Chelsea.