Chris Morgan received a second yellow card on the stroke of half-time after tugging back Fraizer Campbell to spoil a half that the Blades had dominated.
However responded brilliantly in the second period with Stephen Quinn and James Beattie on target to seal the three points.
John Halls’ cross was not dealt with sufficiently by the Hull rearguard and the ball fell to the feet of Quinn (51), who unleashed an unstoppable volley into the top corner.
Hull threw on veteran striker Dean Windass in a bid to claw their way back into the game, but a moment of madness from David Livermore handed the initiative back to the hosts.
Billy Sharp was brought down in the area and Beattie (72) stepped up to lash home the penalty.