United's Under 23s fell to defeat at home to Crewe Alexandra's thanks to two superb efforts from Josh Lundstram either side of Stephen Mallon's equaliser.
Pre-match there was a minute's silence to remember Leicester City chairman Vichai Srivaddhanaprabha and the other four lives in the helicopter accident on Saturday at the King Power Stadium.
United had trialist Wealth Da Silva on show in midfield but in reality it was a quiet opening to the match for both sides until Crewe took the lead after half an hour.
Lundstram picked up the ball outside the box and struck a sweet effort from distance that left Jordan Amissah with little chance.
But United responded well and were level before the break when winger Mallon equalised with a well struck effort of his own.
Playing from the left, Mallon fired a great effort into the corner to ensure United went into half-time with the scores level.
The visitors could have taken the lead once again straight after half-time had it not been for a good, instinctive save from Amissah to push away Lewis Reilly's fierce effort.
Amissah had to be lively again to combine with his defence to block away a stinging Lundstram volley amidst some sustained Crewe pressure at the start of the second half.
United made a triple change for the final half an hour with Under 18 trio Tom Williams, Clark Greaves and Harrison Neal all coming on as the Blades looked for a winner.
But it was the visitors who went back in front, Lundstram scoring his second of the game with another clean finish from outside the box, this time a curling left-footed effort which found the top corner.
Despite some late pressure, United couldn't muster up the necessary chances to find another equaliser and it was Crewe who came closest to extending their lead, but Amissah once again had a solid game in goal.
Blades: Amissah, Sheppeard, Boyes, Doherty, Cantrill, York, Broadbent, Da Silva (Williams 62), Oure (C. Greaves 62), Hallam, Mallon (Neal 62).
Unused: Dewhurst, Ackroyd.