Despite a valiant display against a more experienced Barnsley outfit, United's youngsters slipped to a late defeat at Shirecliffe.
The Blades fielded an extremely youthful line-up, consisting largely of players aged 16 and under, whilst the Tykes fielded several first-year scholars.
The visitors dominated much of the first-half and deservedly went in at half-time in front, but United responded excellently in the second period and equalised in the 58th minute.
Trialist Joe CHEESEMAN volleyed home the loose ball after a corner hadn't been cleared by the Barnsley rearguard.
United looked the more likely winners, with Heh, Calvert-Lewin and Wright all going close, before substitute Bushiri hit a post late on.
Unfortunately, though, the youngsters switched off from a set-piece in injury-time and were duly punished to cruelly deny the home side a share of the spoils.
Coach George Delves summarised the performance: "It was an exciting fixture for many of our youngsters against older and more experienced opposition.
"We were very unfortunate and disappointed to concede a last minute goal that decided the game, having worked so hard to get an equaliser.
"The lads took time to adapt to Barnsley's physicality; we were on the back foot for long periods of the first-half and struggled to handle to continued pressure that was applied on us.
"In the second-half our midfield got a real grip of the game, we enjoyed the majority of the ball and created enough clear-cut chances to win the game.
"Despite switching off from a free-kick that led to the winner, the positives far outweighed the negatives and all the staff are very encouraged for next season."
Blades: Rouse, Charlesworth, Waters, Reed, Evans, Cheeseman, Ramsey (Calvert-Lewin 64), Ishmail, Wright (Slew 84), Cockerline (Bushiri 66), Heh.
Unused: Peace-McDonald, D. Parkin, M. Parkin.