Paul Harsley's youngsters are beaten late on in the Yorkshire Derby.
After a slow and scrappy opening 15 minutes, the Reds begun to take control of proceedings with Victor Adeboyejo heading just over after a great Will Smith cross from the right.
Both Amir Berkovits and Romal Palmer forced the visiting 'keeper into action soon after as Harsley's men looked for the opening goal.
There was a great chance on the half hour mark as Jacob Brown skillfully slipped in his strike partner, but Adeboyejo's fierce shot from 12 yards out whistled an inch wide of the far post with the goalie well beaten.
Berkovits again came close to the opener when on 34 minutes he worked his way into the six yard box but his shot was well parried by the Blades stopper once more.
Other than a handful of corners, the away side had offered very little.
HALF TIME: Barnsley 0-0 Sheff Utd
The game restarted in similar fashion and on 48 minutes Barnsley should have finally taken the lead..
Berkovits robbed his man out on the left flank, burst into the box before cutting the ball back perfectly from the by-line towards the on-rushing Brown, but Jacob's effort was poor, he somehow screwed it well wide from just inside the box with the goal at his mercy.
On 71 minutes another huge chance..
And again it was Berkovits to the fore; he weaved his way into the box, slipped in Adeboyejo and when his effort was charged down by the advancing 'keeper, Berkovits picked up the loose ball and fired a powerful effort at the empty goal but a United defender somehow stretched to clear right off the goal-line!
The visitors then had their first effort on target; a fine, powerful drive from just inside the box which Reds 'keeper Jack Walton turned over spectacularly, one-handed.
But with just over five minutes on the clock, the Blades struck a killer blow..
A cross from the right wasn't closed down and a United man got ahead of his marker at the far post to nod beyond Walton for a late and cruel winner.
FULL TIME: Barnsley 0-1 Sheff Utd
Reds XI: Walton (GK); Smith, Lund, Fielding, Williams; Wardle (Ocran 78), Palmer, Tingle, Berkovits; Brown, Adeboyejo.
Unused: Greatorex (GK), Dolan, Rowe, Greenfield.
