United's U21s slipped to a narrow defeat at the hands of table-topping Derby County at Shirecliffe on Wednesday afternoon.
An unfortunate own goal on the half hour mark from Chris Salt ultimately settled the contest, although the Blades, who included trialist Ferdi Elmas in the starting line-up, fought hard throughout against the league leaders.
Derby enjoyed the better chances in the first half and came close to opening the scoring in the 15th minute when Tom Naylor should have done better with a header at the back post.
The Rams continued to push forward with Gareth Roberts firing over moments later, following good work from Kwame Thomas and Ben Davies.
After Kieron Freeman had hit the post following Saul Deeney's punt forward, the visitors took the lead in the 30th minute when SALT could only deflect Michael Hoganson's teasing cross past Willis into his own net from close range.
The first half drew to a close without any other chances of note with United struggling to get a grip of the game.
The second period, played in foggy conditions, failed to take off at any point, with neither side looking like scoring.
The defeat and aspects of the performance frustrated coach Chris Morgan, who admitted Derby deserved all three points:
"To be honest it was a scrappy affair, there were plenty of tackles made but in truth we never got into the contest, which is disappointing.
"It was a poor game and Derby just about shaded it, although neither side created much with the final pass often being poor.
"We are annoyed that we didn't create more chances and put the back four under more pressure because they were relatively comfortable throughout.
"The goal which ultimately separated the sides was unfortunate, it was one of those balls that as a defender you have to play and it is just unlucky when it squirms into your own net."
Blades: Willis, Westlake, McFadzean, Harriott, Salt, Kennedy, Elmas, Pemberton, Ironside, Philliskirk (Khan 72), Tonne (De Girolamo 56).
Unused: Lynch, J. Williams, Smith.