United's U21s lost for the first time in 2015 against Nottingham Forest at Wilford Lane on Monday afternoon.
A goal in each half for the home side settled the contest in their favour, as the Blades saw their five-match winning run ended against a Forest side in excellent form themselves.
The Blades named three trialists in the starting XI for the fixture. Derby defender Shaun Barker, who has previously worked with Blades boss Nigel Clough, has been given permission to play in two games as part of his rehabilitation from a serious knee injury, started in defence, whilst the other two trialists were Manchester City's Adam Drury, a 21-year-old winger and Josef Shirdel, a German wide player, formerly of Hamburger SV.
After an even first-half, Forest took the lead on the stroke of half-time as REES poked the ball home from Walker's pass.
The second-half was another tight affair, but the Reds made sure of the points in the 78th minute when KELLY scored from a corner at the near post, although the last touch appeared to come off Willis.
Coach Chris Morgan praised his side's effort, but admitted two defensive lapses ultimately proved to be the difference on the day.
He remarked: "It was a decent game and you couldn't fault the effort and desire, in testing conditions, that affected both teams.
"But in the end, the game has been decided on two mistakes from us, which Forest duly punished us for, but we'll be ready to go again in the reverse fixture next Monday."
United: Willis, Drury, Scarisbrick (Kelly 61), Dimaio, Barker (Evans 45), Whiteman, Coustrain, K. Wallace, Shirdel, Cuvelier (Cockerline 69), Hamilton.