United tasted defeat for the first time since January after going down 3-0 on Tyneside against Newcastle United.
Following a goalless first-half, the game turned six minutes into the second stanza when John Egan was dismissed for a second yellow. The home side seized their opportunity, netting three times through Allan Saint-Maximin, Matt Ritchie and Joelinton.
Boss Chris Wilder made one change to the side which drew at Aston Villa with John Fleck fit again to take his place in midfield, as John Lundstram dropped to the bench.
Striker Richairo Živković was also named amongst the substitutes, but Jack O'Connell and David McGoldrick narrowly missed out through injury.
Both teams again took the knee in support of the Black Lives Matter movement in another powerful statement, whilst a period of silence also took place just before in memory of those who have lost their lives to COVID-19.
United began brightly with Ollie Norwood's first minute free-kick making Newcastle 'keeper Martin Dubravka work as he fisted a dangerous cross clear under pressure.
On six minutes after a cross from Enda Stevens was deflected behind for a corner, Norwood's deep delivery just eluded Jack Robinson who ghosted in around the back.
After the Blades dominated the opening 10 minutes, the hosts eventually grabbed a foothold. It was from the Magpies' first corner where an opening almost occurred as the ball stuck inside the area prompting a scramble which ended with the Blades clearing the danger. The hosts then worked the ball down the right for the dangerous Saint-Maximim to drive into the area, but his cut-back landed between two black and white shirts.
With 12 minutes gone United created another half chance after good work down the right. George Baldock's cross found the head of Oli McBurnie but his connection was weak as his effort was gathered by Dubravka.
A minute later and Dean Henderson was called into action for the first time. The ball was worked into the path of Ritchie to strike from range, but the United stopper flung his way to his left to make a good stop.
Newcastle created the best chance of the half on 17 minutes. A swift counter which began deep inside their own half was taken on by Miguel Almiron who sprinted into United territory before sliding in Joelinton who was through on the angle. The finish though was lacking as the striker scuffed his effort harmlessly towards goal after kicking the ground when attempting to finish.
Egan blocked a goalbound effort from Jonjo Shelvey as Newcastle began to enjoy a strong period in the game, but following the drinks break, Wilder's side came back into the contest. Again, it was good work down the right involving Sander Berge and Baldock which ended with the latter crossing for Billy Sharp, but the striker fired over first time with an effort form 18-yards.
Referee David Coote reached for his pocket for the first time when Egan and Joelinton were cautioned after a minor scuffle.
Just before the break a Fleck corner was met by Egan at the back post, but Newcastle got the luck of the bounce as they smuggled the loose ball clear.
Just six minutes into the second half, United found themselves down to 10 men. The Blades were on the attack when Fleck attempted to seek out Sharp. Newcastle cleared long downfield, with Egan challenging with Joelinton. The luck of the bounce favoured the Newcastle striker and as he attempted to sprint clear, he was pulled back by the Irishman who was given his marching orders for a second bookable offence.
Soon after the Blades were behind. Ritchie played in a low cross which looked innocuous, but Stevens missed the ball completely when attempting to clear first time allowing Saint-Maximin, lurking just behind, to drill the ball beyond Henderson.
The Blades responded well to going behind and came close to levelling the game soon after. Sharp produced some fine build up play to swing a great ball wide to Baldock. The wing-back steadied himself before delivering deep towards the back post where Sharp had sprinted into the box, but headed wide of Dubravka's near post.
At the other end Almiron should have done better after being teed up by Saint-Maximin, as Wilder made the first change with Lundstram replacing Berge.
Despite being a man light, United looked comfortable but any momentum was disrupted with the home side's second goal. Ritchie advanced forward from deep, with Newcastle holding a 2v1 against Baldock, the Scotland international opted to go for goal himself, firing a stinging 22-yard strike beyond Henderson.
United refused to lie down and almost cut the deficit. Sharp showed determination to win the ball inside the Newcastle area before driving to the by-line. He cut the ball back for the advancing Stevens, but he blazed over after connecting with a shot from just inside the area.
Wilder gave Zivkovic a debut from the bench, replacing Sharp whilst Luke Freeman also came on for Fleck.
The changes didn't turn the tide though and Newcastle sealed the game with a third on 78 minutes when Almiron's low cross was converted by Joelinton.
Wilder made a further change before the end with Kieron Freeman replacing McBurnie. The Blades had the last meaningful opportunity of the afternoon when Chris Basham's dangerous low cross just eluded the outstretched leg of the advancing Zivkovic.
Newcastle: Dúbravka, Manquillo, Fernández, Lascelles, Rose, Hayden, Shelvey (Schär 85'), Ritchie (Yedlin 90'), Almirón (Lazaro 85'), Saint-Maximin (Bentaleb 79'), Joelinton (Carroll 79').
Subs: Darlow, Gayle, Muto, Krafth.
Blades: Henderson, Baldock, Stevens, Fleck (L. Freeman 74'), Basham, McBurnie (K. Freeman 84'), Sharp (Zivkovic 74'), Egan, Norwood, Robinson, Berge (Lundstram 66').
Subs: Jagielka, Mousset, Osborn, Moore, Rodwell.