Despite a spirited performance, particularly in the second-half, United's U21s slipped to defeat at The Valley on Monday afternoon.
Goals in early in each half from Harry Lennon and Kadell Daniel respectively, proved to be enough for the Addicks, although United dominated the last half hour of the game and deserved a goal at the very least for their efforts in dreadful conditions in the capital.
Chris Morgan's team included two trialists in the shape of Jordan Hendrie, who completed a full game on the right-wing and striker Scott Fenwick who featured in attack.
United started brightly, but fell behind in the 10th minute when LENNON reacted first to lash the ball home from close-range after Willis had fumbled a free-kick.
Charlton nearly doubled their lead moments later, hitting the bar with a long range effort, before Reed's deflected shot was parried wide by Pope in the home goal.
The Blades had further half chances in the first period with Dimaio stinging the palms of Pope with a rasping drive from 30 yards out.
Charlton were quickly out of the traps again in the second-half and doubled their lead in the 55th minute, when DANIEL took full advantage of an opportunity inside the visiting penalty area.
Sam Berry replaced returning skipper Terry Kennedy just after the hour and Khan perhaps should have done better when clear inside the box, but he was denied low down by Pope, Hendrie than saw his effort blocked at the back post after good play by Hamilton on the left.
United piled on the pressure as the game progressed, Dimaio was the next to have a shot saved by the assured Pope.
Wright and Coustrain were introduced, replacing Fenwick and Dimaio and in the latter stages, Reed was only denied a shot on goal by a last-ditch tackle from Thomas, whilst both Khan and Hamilton had further opportunities, but in the end Charlton saw the game out without any notably incidents.
Blades: Willis, Paling, Scarisbrick, Dimaio (Coustrain 74), Kennedy (Berry 61), Banton, Hendrie, Reed, Hamilton, Fenwick (Wright 72), Khan.