United's Under 23s fell to 3-1 defeat at home to Burnley in their final match before Christmas as Stephen Mallon's first half equaliser ended as the highlight in what was an evenly fought game.
It was a much closer encounter than the 6-0 defeat in the reverse fixture earlier in the season and on another day United could have got a result.
Kean Bryan, Daniel Lafferty, John Lundstram, Kieron Freeman and Tyler Smith all got starts in a very different looking line-up.
It was the Blades who had the better of the opening exchanges, Reece York testing England international Nick Pope with a header before Kean Bryan curled a free-kick on target which didn't overly trouble the goalkeeper.
But United were caught out moments later when Burnley captain Dwight McNeil won a 50/50 with Smith in the middle of the park, the midfielder drove forward and unleashed an unstoppable effort into the top corner from well outside the box.
United then rode their luck as Burnley pushed for a second, Dan Agyei coming close twice when he curled wide before slamming the post from an acute angle.
The Blades though did respond shortly before half-time, some neat football allowing York to cross, Lafferty kept the ball in play before Mallon smashed the ball past Pope from close range to level the scores.
Frustratingly though United couldn't take a draw into half-time. Deep into first half stoppage time, Jake Eastwood spilled a McNeil effort wide for a corner, a slip which cost United as Agyei turned the ball home from the resulting cross into the box.
United did their best to respond after the break and Lafferty saw an effort cleared off the line just moments before Burnley killed the game off.
It was another goal of United's own undoing as Freeman was caught trying to get on the end of a short pass back to him, allowing the pacey Agyei to nip in, run towards goal and slot beyond Eastwood.
United continued to push in an end to end encounter, Mallon going agonisingly close to a second with a curling effort before substitute Simeon Oure was denied at close range, the striker going close again when he headed Lafferty's cross just wide with five minutes to go.
Blades: Eastwood, Belehouan (Ferguson 75), Bryan (Oure 65), Doherty, Graham, York (Greaves 75), Freeman, Lundstram, Smith, Mallon, Lafferty.
Unused subs: Dewhurst, Sheppeard.