Bradley Johnson's late goal grabbed Leeds their first win over Yorkshire rivals Sheffield United in 17 years in front of the npower Championship's biggest crowd of the season.
The Leeds midfielder converted second-half substitute Robert Snodgrass's cross in the 84th minute to settle a disappointing encounter that ignited in the final 10 minutes.
Snodgrass, in only his second appearance this season, was sent off in the 89th minute for his second yellow card and Leeds were then saved by the woodwork in time added on.
Nick Montgomery's curling cross was met by Jon Ertl and, with Leeds goalkeeper Shane Higgs beaten, the ball came back off the crossbar.
There was still time for Blades substitute Jamie Ward to be shown a straight red card for a reckless late challenge on Neil Kilkenny.