United's youngsters slipped to defeat against Charlton Athletic at the SteelPhalt Academy on Saturday.
Two second-half goals for the Addicks saw them leave Shirecliffe with all three points, despite a spirited display form the young Blades.
Lead Coach Derek Geary remarked: "Again we fielded a very young side and they're getting some vital experience.
"We looked a threat on the break, but in the end Charlton made their experience and physical present count and we must learn again and look to improve further in the coming weeks."
United were forced to defend for period of the first-half, but Swaine and Greaves looked a live threat on the counter attack.
Goalkeeper Warhurst was called into action twice from distance in the first period, as the Blades restricted the visitors to long-range efforts.
But in the 54th minute, the Addicks took the lead from a corner, converting with a header at the back post.
And despite United pushing Charlton back in the final ten minutes, it was the visitors who netted a game clinching second in the latter stages.
Blades: Warhurst, Robinson, Belehouan, Ferguson, Foulstone, Greaves, Ompreon (Potts 54), Broadbent, Hakwes, Lawrence (Mason 54), Swaine (Ackroyd 65).