United's U18s slipped to defeat against Nottingham Forest at Wilford Lane on Saturday, despite producing a spirited performance.
A goal in each half proved to be enough for the Reds, who managed the game well, despite United's best efforts.
Forest started brightly and had the Blades on the back foot in the opening minutes by putting a number of crosses into the visiting penalty area.
As the first-half progressed, United began to get a foothold in the game, but in the 24th minute, the home side opened the scoring following good play down the left-wing.
For the remainder of the half United enjoyed the majority of possession, but struggled to create any clear cut chances, with Forest looking a threat on the break.
The visitors started the second-half positively and began to pile to the pressure on the home side in search of an equaliser and just after the hour Mallon fired just wide with the goal at his mercy.
Forest remained resolute though, rebuffing United's advances to restore parity and they made then game safe in stoppage time, capitalising on a mix-up in the visiting defence to net the decisive second.
It was harsh on the Blades, who produced a battling performance, but ultimately it was the home side that took their chances to net the victory.
Blades: Perryman, Charlesworth (Ford 81), Mallon, Gilmour (Slew 74), Adebowale, Semple, Maw, Gordon, Litchfield, Cummings, Smith (Hallam 68).
Unused: Warhurst, Ramsey.