Alex Neil’s side held their own for the opening 30 minutes before Dan Neil was shown a straight red card and defender Anel Ahmedhodzic headed the hosts ahead.
The Blades then made it 2-0 shortly after half-time after a close-range finish from Max Lowe.
Sunderland responded well and pulled one back through Lynden Gooch but weren’t able to take anything from the game.
Our chief Sunderland writer Phil Smith has dished out his player ratings from the match:
5. Dennis Cirkin - 6
Didn’t have a great deal of chance to go forward and was steady again in his defensive work. Sunderland struggled in the early period of the second half to pick up Ahmedhodzic as he overlapped down the right, but they dug in and hung on for the most part. 6 Photo: Frank Reid
6. Jack Clarke - 5
One or two dangerous runs early on but his influence understandably waned after the red card. Looked a little exposed defensively early in the second when Sheffield United were dominant. 5 Photo: Martin Swinney
7. Dan Neil - 4
Started really brightly in the holding role usually reserved for Corry Evans, moving the ball well and picking up good positions. Caught on the ball on the half hour mark near his own box, shown a straight red card for hauling down McAtee as a result. The visitors were ahead less than a minute later. A tough lesson. 4 Photo: Frank Reid
8. Elliot Embleton - 6
Was tidy through the early stages and got through the bulk of his defensive work well enough in a more withdrawn role than he is used to. 6 Photo: FRANK REID