Sunderland moved to within five points of an automatic promotion place after overcoming the Blades for a third time this season.
The Black Cats stretched their unbeaten run at the Stadium Of Light to 19 matches with goals from Tommy Smith, Gary Breen and substitute Kevin Kyle in a fiery clash.
United have now taken just one point from their last four games and unless there is a dramatic improvement in results, are in danger of missing out on the play-offs.
Smith grabbed his eighth goal of the season after seven minutes, sweeping home a right wing centre from skipper Jason McAteer at the near post.
The lively Smith, again preferred to leading scorer Marcus Stewart, almost added a second ten minutes later after he had worked his way along the byline.
The visitors came into the game and after keeper Thomas Myhre, in for the injured Mart Poom had dropped a deep centre, Robert Page scooped a dangerous free-kick from Alan Wright over the bar.
Wright then tested Myhre with a powerful free-kick, while at the other end the trickery of Smith almost led to a second home goal as his great pass just needed the finishing touch in front of an open goal.
The Blades stepped up the pace after the break and, following a spell of intense pressure, Mark Rankine fired wide.
Carl Robinson, making his home debut, surged into the United penalty box and looked a certain scorer only to be denied by Paddy Kenny.
But with Sheffield United boss Neil Warnock waiting to make a double substitution in the 65th minute, Sunderland went further ahead when central defender Breen headed home Sean Thornton's corner kick.
Thornton went clear but his shot failed to match his run, before Phil Babb denied the visitors with a last-ditch tackle on Jack Lester and Myhre made a great save from Michael Tonge in the 90th minute.
Kyle however made certain of all three points when his left foot shot gave Kenny no chance in injury time