United's U23s had their play-off hopes ended with a defeat away to Charlton Athletic on Monday afternoon.
A second-half goal from Louis-Michel Yamfam was enough to end the Blades six game unbeaten run at The Valley.
The hosts almost took the lead on 25 minutes as Yamfam picked up the ball from distance, let fly and cracked the post before the Blades cleared to safety.
United played well without really creating much and the only chance of the half came when trialist Crankshaw fired just wide of the post after some good work to get into the box.
Just after the hour mark the deadlock was broken as Dempsey broke down the left wing and sent in a low cross for YAMFAM to convert at the second time of asking as his initial effort was kept out by Warhurst.
United substitute Oure came close to restoring parity with 15 minutes remaining but his effort was off target from inside the area.
As the clock ticked over 80 minutes the Blades came agonisingly close to an equaliser but Crankshaw's header hit the post from a Portman cross and Charlton held on for victory.
Blades: Warhurst, Portman, Cantrill, Ferguson, Doherty, Semple (Broadbent 65), Gilmour (Graham 69), Slater, Smith, Yates (Oure 74), Crankshaw.
Unused: Weaver, Brown.