All three of United’s goals in the U21 Professional Development League Two fixture came after the half-time interval.
The first arrived six minutes after the restart, when Blues failed to clear their lines properly following a corner and Julian Banton drilled a loose ball home following a goalmouth melee.
Blues then had several opportunities to restore parity, but George McGee, Koby Arthur and Liam Truslove all squandered decent chances.
With just over an hour on the clock, the referee adjudged that Blues keeper Connal Trueman had fouled Joe Ironside as the Blades striker chased down a long ball and pointed to the spot.
Ironside stepped up to take the penalty himself and made no mistake as he sent Trueman the wrong way, and at the same time fired his side into a two-goal advantage.
It was game over for Blues on 77 minutes when Callum McFadzean’s superbly hit volley from the edge of the area found the back of Trueman’s net.
Blues coach Steve Spooner admitted it was a fair result, although he felt the scoreline slightly flattered the hosts.
“They had the better chances and worked the keeper more than we did, but the scoreline probably did us a little bit of a disservice,” said Spooner.
“Attacking-wise when we got in and around the 18-yard box, we either took too many touches or made the wrong decisions and lost the opportunity.
“On the day they were stronger than us, created more opportunities and were more clinical in their finishing.”
Despite seeing his side concede three goals, Spooner felt that his 17-year-old goalkeeper Connal Trueman (pictured) was his team’s standout performer.
“Connal was excellent and made some outstanding saves,” he added.
“Without him the defeat could have been even bigger.”
Blues U21s: Trueman, Higgins (Cogley, 83), Moseley, Webb, Bell, Kelly, Sutherland (McFarlane, 62), Truslove, Hales (Deadfield, 73), Arthur, McGee.