An equaliser deep, deep into injury time prevented Town's youngsters going through to a quarter-final with either Manchester United or Nottingham Forest. Town had gone ahead through Robert Dickinson just after the half hour, but couldn't hold their lead.
In a game of few chances the Blades were in the ascendent during the first period while Town ran the show in the second. The away side could have gone ahead early on when a neat lay-off inside the penalty area from Lewis Killen was shot goalward by Ryan Mallon. Town keeper Darren Kelly averted the threat.
Robert Nugent and Lee Featherstone also went close for the away side with the former heading powerfully wide from one of several corners
Town's star striker Darren Bent received a yellow card for a few words with the referee and wasn't getting too many opportunities.
As the half wore on Town started to make more of an impression and just after the half hour Robert Dickinson scored as good a goal as you'll see. A cross from the left went beyond the far post where he picked the ball up, went inside the defender and hit the ball home to give Town the lead at half-time.
The second half was largely incident free and scrappy. Both sides lost the ball constantly and there were few decent chances. United seemed to have run out of ideas and time was well and truly up when a cross from the right was scrambled home by Robert Nugent with at least one other Sheffield United player in attendance.
When the whistle went another two minutes later the Blades players embraced while Town's lads kicked the air. A replay at Bramall Lane, date to follow.
Not the best performance from the youngsters in the driving rain, but they were certainly better in the earlier game against Leicester and in the second half against Crystal Palace.
Town team: Kelly, Artun, Beevers (Chaffey), Bonwick, Snowdon, Westlake, Bloomfield, Ambrose, Bent, Richards, Dickinson (Burton).
Richard Logan scored the first goal of his loan spell at Cambridge in their 2-0 away win at Adams Park, Wycombe. The Town striker scored the first goal after 19 minutes.