Manchester City loan pair James McAtee and Tommy Doyle scored the goals that set Sheffield United back on the Championship promotion trail.
The two midfielders struck after Edouard Michut's first goal for Sunderland had put the home side ahead, against the run of play.
The three points allowed the Blades to take advantage of the fact that Middlesbrough dropped points in a draw with Stoke City 24 hours earlier and open up a six-point lead in the race for the second automatic promotion spot.
The Black Cats began the night hoping to build on their fine win at Norwich City at the weekend and boost themselves back into the play-off reckoning, but they ended up slumping to a fourth defeat in their past five league games.