United's unbeaten Premier League away run came to halt despite another impressive showing, as the Blades were beaten 2-0 by Manchester City.
After Chris Wilder's side were denied a first-half lead by VAR, two goals in the second stanza from Sergio Aguero and Kevin De Bruyne sealed the points for City, who were tested throughout by a spirited United display.
Wilder made three changes from the side which drew with Watford on Boxing Day with Mo Besic replacing the injured John Lundstram for his first Blades Premier League start, whilst there was a change to the front two as Oli McBurnie and David McGoldrick made way for Lys Mousset and Callum Robinson.
United started brightly against the champions earning three corners inside the first 10 minutes as Pep Guardiola's side were forced to answer some early questions.
On eight minutes the Blades created the first real opening of the contest. Robinson was alive to a quickly taken throw when he spun to loop an inviting cross into the area, Mousset attacked the ball but glanced his header wide from eight yards.
United were tested for the first time on 17 minutes when Riyad Mahrez beat the offside trap to latch onto a through ball down the right of the area. He collected the pass before cutting inside but his effort from an acute angle was eventually blocked by John Egan, and United cleared the resulting corner.
City began to dominate the ball and the Blades were thankful to Egan again after he blocked a long-range effort from Rodrigo.
At the other end Mousset fired an effort towards goal after breaking down the right. His shot looped over the bar after taking a deflection, and after the resulting corner was cleared, Egan then headed over under pressure as he connected to the returning cross.
The Blades were then denied an opening goal after a call from VAR. John Fleck, making his 150th United appearance, picked up the ball deep inside his own half, he surged forward before placing a terrifically weighted pass into the path of Mousset who coolly netted. The decision went to VAR and it deemed the Frenchman was marginally offside.
Seven minutes before the break and the Blades cut City open down the left after some terrific play from Fleck and Jack O'Connell. The move ended with the overlapping centre half turning the ball around the corner for Enda Stevens, he crossed towards the back post but Besic blazed over on the volley.
The Blades created another great chance just five minutes before the break. Fleck coolly played himself out of a tight spot deep inside his own half. He found Ollie Norwood on the edge of his own area, who then played a wonderful long-range pass to free Mousset. The striker sprinted in on goal but from the angle he nudged the ball into the side netting in an attempt to beat the onrushing Claudio Bravo.
Before the break Oleksandr Zinchenko fired well over from range, as City failed to find a way through United's defence in the first 45.
After another solid opening by the Blades, the hosts took the lead amid protests from those in red and white. On 55 minutes Norwood fed a pass into Fleck, the Scottish international appeared to lose possession after being accidently blocked by the official. City then pounced on the loose ball as De Bruyne slid the pass into Aguero who clinically rifled the ball beyond Henderson. United players immediately protested by after a VAR check, the goal stood.
The Blades reacted positively and soon after Mousset was in at the other end after a barnstorming break from Chris Basham. Just when it looked like the striker was through, Bravo raced out to smother the ball, whilst the flag had also been raised for offside.
Boss Wilder acted to make the first change just before the hour as Robinson made way for David McGoldrick.
United started to pour forward in search of an equaliser but couldn't find the break after some fine build up play. For a time, it was end-to-end, with Fleck tracking back to make a vital interception as City almost countered.
Egan continued to be a heroic last line of defence when he made another inspired block to deny Mahrez who cut inside to fire on goal, only to see the Republic of Ireland international make a terrific last-ditch block.
The Blades carried a real threat of an equaliser, with Wilder throwing caution to the wind with the introduction of McBurnie for Besic.
With United forced to take chances, the hosts eventually capitalised with the killer second goal. Mahrez produced the dancing feet to create the space before slipping De Bruyne in on goal and the Belgium international calmly slotted beyond Henderson for 2-0.
The Blades were denied a deserved consolation in stoppage time when somehow sub Billy Sharp's header from eight yards hit the inside of the post and rolled along Bravo's line to safety.
Man City: Bravo, Walker, Garcia, Fernandinho, Zinchenko, Rodrigo, Bernardo (Gundogan 62'), De Bruyne, Sterling (Jesus 88') Mahrez, Aguero (Foden 80').
Unused: Carson, Mendy, Cancelo, Otamendi.
Blades: Henderson, Baldock, Stevens, Fleck, O'Connell, Basham, Robinson (McGoldrick 59'), Egan, Norwood, Mousset (Sharp 82'), Besic (McBurnie 75').
Unused: L. Freeman, Jagielka, Verrips, Osborn.
As it happened...
First ball into the United area is initially dealt with by Basham and then collected by Henderson. 0-0.
United make a foray forward through Mousset, and his centre is put behind for a corner.
Norwood's delivery though is headed clear. 0-0
De Bruyne squeezes in a cross from the by-line but Besic is well placed to sweep clear for United. 0-0.
Sweeping Blades move involving Mousset, Fleck, Robinson and Baldock ends in winning a corner.
The first is headed behind off a City player, the second one goes deep to the back post and is cleared. 0-0.
Chance for United!
A quick throw is put into a dangerous area by Robinson but Mousset glances his header wide from eight yards. 0-0.
Crucial block by O'Connell as De Bruyne attempts to cut the ball back from the by-line. 0-0.
Some very cool play at the back from Henderson and Stevens sees United play out from deep as Besic plays the ball out to the right. The attack comes to nothing but some good play from the Blades under pressure inside their own half. 0-0.
First real chance for City as Mahrez is played in down the right of the area, he cuts inside to shoot but Egan is there to block. 0-0.
De Bruyne takes aim from 25 yards but fires the ball straight into the chest of Norwood who takes it well! 0-0.
Egan with another crucial block as he throws himself at Rodrigo's long-range effort. United under pressure but holding firm. 0-0.
Mousset's deflected effort loops over for a corner. After City clear, the ball is turned back in towards Egan who heads over. 0-0.
Goal for United is ruled out by VAR.
Fleck with a surging run forward, he then puts in a wonderful ball in behind for Mousset who collects, steadys himself and fires low into the net. VAR then intervenes and City have a free-kick.
Sterling's deflected effort goes wide of Henderson's near post.
De Bruyne's corner goes to Zinchenko, he plays it to ex-Blade Walker who fires well over. 0-0.
Some great play from United involving Fleck, O'Connell and Stevens ends with a cross to the back post which is bazed high and wide on the volley by Besic. 0-0.
Chance again for the Blades.
Fleck plays out deep inside his own half. Gives it to Norwood who goes long for Mousset to run onto, he sprints into the area on the angle, but toe pokes it into the side netting. 0-0.
United scramble clear a Sterling cut-back from the by-line as City threaten down the left. 0-0.
One added minute
Zinchenko fires over wildly from 20 yards.
Man City 0-0 Blades
United doing well and would have been in front but Mousset's goal ruled out by VAR.
Here we go again, second half underway.
De Bruyne with the first effort of the second half when his shot sails over from 25 yards. 0-0.
Ball over the top and Mousset is onto it again, he wins the footrace, before sliding a pass inside for Besic who takes a touch before firing just over from the edge of the area. 0-0.
Goal for City.
Controversy here as the official appears to get in the way of Fleck as he attempts to receive a pass from Norwood. The loose ball is picked up by City, the ball is slid into Aguero who nets clinically. 1-0 City.
Basham with a surging run forward, he slides the ball into Mousset who looks in, but Bravo comes out to smother and in the meantime the flag is raised for offside. 1-0 City.
Bernardo Silva into the book after pulling down Fleck.
First change for United as Robinson is replaced by McGoldrick.
Bernardo Silva replaced by Ilkay Gundogan.
End-to-end stuff here as United throw bodies forward, and City almost hit the Blades on the counter but for a brillant Fleck interception. 1-0 City.
Egan with another terrific block as Mahrez stepped inside to shoot inside the area. VAR check for handball is quickly waved away and United clear the corner.
Mahrez upended by Egan as he tries to collect a one-two.
Free-kick 22 yards out is then blazed over by De Bruyne.
Besic replced by McBurnie.
Foden replaces Aguero.
There may have been a yellow there for Aguero for time wasting as he exited the pitch.
Goal for City.
United caught on the counter as they have to throw bodies forward. A swift move sees Mahrez ride a couple of tackles before playing in De Bruyne wh nets. 2-0.
Sharp replaes Mousset.
Yellow for Stevens as he halts Foden on the attack.
Gabriel Jesus is on for Sterling.
Four added minutes
Sharp so unlucky as his header from eight yards hits the inside of the post and rolls along the line to safety.
Man City 2-0 Blades
Goals from Aguero and De Bruyne deny a spirited Blades who had a Mousset opener chalked off by VAR.