United's Under 23s suffered their first defeat in the Premier League Youth Cup to Everton, but it wasn't without a fine effort from a young Blades side.
Antony Evans' first half free-kick was the difference but United were the better side during the second period the match and should have equalised in stoppage time when substitute Harry Boyes hit the crossbar.
Everton, who came into the game having won their opening two matches like United, started on the front foot and could have been ahead inside the first two minutes when Josh Bowler fired just wide when cutting in from the right.
Just as United were getting a foothold in the game midway through the first half, Everton struck what would turn out to be the killer blow.
A foul on the edge of the box gave forward Evans the chance to step up and curl a neat free-kick over the United wall and past the stranded Marcus Dewhurst.
United though came out fighting after half-time and Simeon Oure had the first half chance when he fired over from distance after good work from Stephen Mallon.
A bigger chance would come for Mallon himself just minutes later. Some fine one-touch football from United saw Kalinauskas set up Mallon but the winger saw his goal-bound shot blocked at close range.
Evans had a chance to double Everton's lead but was denied well by Dewhurst before more excellent football from the Blades presented a chance to Oure, but his effort was also saved.
Harry Boyes and George Broadbent were introduced inside the final 15 minutes as United pressed for a crucial equaliser, and Boyes almost got it when he came closest of all in stoppage time.
More good work from Mallon down the left offered a shooting opportunity and when his shot was blocked the rebound fell to Boyes on the penalty spot, but the substitute's effort came agonisingly back off the bar and dropped the wrong side of the line.
Defeat still leaves United with a good chance of progression from the group after picking up six points from their opening three games.
Blades: Dewhurst, Belehouan, Williams (Boyes 78), Doherty, Cantrill, York (Broadbent 84), Sheppeard, Oure, Young, Kalinauskas, Mallon.
Unused subs: S. Kelly, Gordon, Neal.