United's youngsters suffered their first defeat of the season at the hands of Wigan Athletic on Saturday.
Second-half strikes from Ottis Khan and Jake Eyre and an improved performance after the break were positives for the visitors, but doubles from Omar Thompson and Joey Johnson paved the way for a home win.
The away side started positively, but Wigan's imposing defence kept United's attacking threat at bay. In the sixth minute Lynch had to save smartly from Thompson, but moments later he was powerless to deny fellow striker JOHNSON.
The Blades were lucky not to fall further behind when Johnson and Bradley Anderson combined, before the latter hit the woodwork with Lynch beaten.
United were struggling to contain their more experienced opponents and Thompson was the next to test the goal frame, but the visitors held on for half-time.
The respite didn't last for long though - after the restart as THOMPSON doubled the Latics lead from a Johnstone free-kick.
United responded positively and in the 53rd minute, KHAN whipped in a free-kick from the left, which deceived everyone and drifted in at the back post.
Just after restoring their two-goal advantage through THOMPSON, the home side were reduced to ten men when Kerwin saw a straight red card for a nasty lunge.
The Blades gave themselves a lifeline as injury-time approached when EYRE rose highest to head home at the back post, but hopes of snatching a draw were extinguished moments later when JOHNSON beat Lynch to a high ball and subsequently tapped home.
Blades: Lynch, Payling, Ptak, Whiteman (McDonagh 54), Scarisbrick, J. Williams, Khan, Dimaio, Smith (Eyre 76), De Girolamo, Heather (Coustrain 67).