United's U23s suffered a disappointing defeat at Birmingham City on Wednesday evening.
A first-half brace from Nicolai Brock-Madsen put the hosts in the ascendency and Kyle McFarlane rounded off the scoring at St. Andrew's.
Goalkeeper Simon Moore played 90 minutes, whilst Ben Heneghan and Nathan Thomas also played full games.
Just five minutes had gone when the hosts took take the lead. BROCK-MADESN turned home a drilled cross out from Seddon.
And the Blues came forward again on the quarter hour mark with Bailey's strike forcing a good diving save from Moore following O'Keefe's lay-off.
On the half hour City broke and McFarlane should have done better when firing over having found space for a shot. At the other end, Hallam latched on to a diagonal ball and looked to have restored parity, but his lofted effort was cleared off the line by Seddon.
Before the break, City put themselves firmly in control, as BROCK-MADSEN headed home from on the penalty spot from Martin's cross.
The Blades probed for much of the second period, but struggled to seriously troubled City's defence. Hallam fired a free-kick just wide and then a last-ditch block denied Smith a route to goal.
But with 20 minutes remaining the game was put to bed as MCFARLANE added a third for the home side, sliding past Moore from Lakin's through ball.
Blades: Moore, Bennett, Thomas, Graham, Heneghan, Ferguson, Gilmour, Slater, Smith, Hawkes (Greaves 45), Hallam.
Unused: Warhurst, Cantrill, Potts, Lawrence.