United's U21s slipped to defeat against league leaders Huddersfield Town at Canal Side on Monday afternoon.
After Febian Brandy had given the Blades a first-half lead, second-half goals from former United loanee Harry Bunn, who has netted for Chris Morgan's side earlier in the season, and a late header from Paul Mullin saw the spoils stay in West Yorkshire.
The Blades started brightly and took the lead in the eighth minute. Florent Cuvelier combined with Jasper Johns down the left, before Brandy got across his marker to apply the finishing touch to the pinpoint cross.
United went on to control much of the first-half, with Huddersfield limited to just a couple of goalscoring opportunities, although they did have a lot of possession.
Town equalised in the 51st minute, when BUNN fired home into the top corner from just inside the penalty area.
The hosts were clearly buoyed by restoring parity and kicked on looking for that elusive winner. It duly came in the 77th minute, when the Terriers broke United's dogged resistance. MULLIN rose highest to head home Sinnott's inswinging corner from the left.
In the final ten minutes United tried in vain to get back into the contest, but ultimately fell to defeat as Town made it eight wins from nine outings to cement their position at the top of the league.
Speaking after the defeat, coach Chris Morgan was frustrated the Blades failed to build on a sound opening 45 minutes: "Ultimately I am bitterly disappointed with the defeat because we simply didn't do enough to win the game.
"I said at half-time that we were starting to allow Huddersfield back into the game and in the second period we just sat back and the game passed us by. They are top for a reason, but having taken the lead we should have kicked on and taken something from the contest.
"Florent (Cuvelier) did well and was keen to get on the ball and make things happen, but overall we didn't apply ourselves well enough."
Blades: Howard, Hodder (Dimaio 81 Jean-Francois (Khan 59), Cuvelier, Kennedy, McGinty, Smith, Reed, Taylor, Brandy (Calvert-Lewin 81), Johns.