United's U23s exited the Premier League Cup at the last 16 stage, following a narrow defeat to Portsmouth on Monday evening.
Pompey's Nicke Kabamba scored the only goal of the game with ten minutes remaining at West Leigh Park, home of Havant & Waterlooville, despite a spirited performance from a youthful Blades side against experienced opposition.
The home side started brightly and forced a couple of early corners, but United defended well. The first scare of note came when Kelly deflected a Davies cross over the bar.
Portsmouth enjoyed more possession in the opening 45 minutes, without ever seriously looking like breaching the Blades defence. In response, Hirst fired over O'Brien's goal from distance.
Before the break, Perryman was called into action twice in quick succession, producing good saves to deny Kabamba and then Chaplin.
The Blades were out of the blocks quickly in the second period and O'Brien was at his best to deny Gilmour after good work by Wright. At the other end, Perryman was out smartly to dive at the feet of Kabamba.
The tie had become an open affair and it was the hosts who secured a quarter-final spot with a goal in the 80th minute. Perryman couldn't gather Lowe's shot and KABAMBA reacted quickest to convert the rebound to send Pompey into the last-eight.
Blades: Perryman, Bennett, Kelly, Cantrill, Charlesworth, Harrington, Slater, T. Smith, Gilmour, Hirst (K. Smith 76), Wright
Unused: Warhurst, Ford, Ferguson, Greaves.