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, the Blades, who still harbour hopes of gatecrashing the play-offs, responded brilliantly in the second period with Stephen Quinn and James Beattie on target to seal the three points.
Lee Martin returned to United's bench for the first time since February after finally overcoming a troublesome knee injury and John Halls replaced Derek Geary in defence.
David Livermore came in for the injured Wayne Brown at the heart of Hull's defence, while Campbell and Caleb Folan were given another chance to let their burgeoning partnership flourish in attack.
It was Campbell who created the first opening after six minutes, as the on-loan Manchester United striker spun his marker with consummate ease before seeing his curling effort thwarted by Paddy Kenny.
This appeared to spark the Blades into life and Michael Tonge was only a matter of inches away from giving them the lead after 16 minutes.
The midfielder latched onto Craig Fagan's misplaced pass in the middle of his own half before setting off on a swashbuckling run, which culminated in his fierce left-foot drive arching narrowly over Boaz Myhill's crossbar.
United continued to press as the half wore on with top scorer Beattie clipping a shot over the crossbar and Billy Sharp heading wide after making a late surge into the penalty area.
Hull had shown little in the way of attacking threat but they wasted a golden opportunity to go in front just before the half hour mark.
The ball fell invitingly to the unmarked Dean Marney 15 yards out after a goalmouth scramble, but the former Spurs midfielder skewed his volley agonisingly over the crossbar.
Blades striker Sharp has endured a miserable season in front of goal and it was easy to see why as he inexplicably headed over from David Cotterill's teasing cross five minutes before the break.
Kevin Blackwell's side were dealt a hammer blow on the stroke of half-time when Morgan received his second yellow card for hauling back Campbell with the diminutive striker through on goal.
Pre-empting the expected Hull onslaught Blackwell sacrificed Cotterill at the break, replacing him with veteran defender Ugo Ehiogu.
But it was the Blades who started with the more obvious vigour at the start of the second period and they were only denied the lead through a breathtaking save from Myhill.
Sharp angled a fierce header towards the far post from Tonge's cross but the Welsh stopper sprung to his left to claw the ball away.
There was little he could do about United's opener a few minutes later, though, as Quinn produced a goal completely out of keeping with what had gone before.
Halls' cross was not dealt with sufficiently by the Hull rearguard and the ball fell to the feet of the Irishman, who unleashed an unstoppable volley into the top left-hand 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 Livermore handed the initiative back to the hosts after 72 minutes.
Sharp drew a rash tackle from the former Millwall defender after surging into the area and James Beattie stepped up to lash home his 22nd goal of prolific campaign to put the Blades out of sight.
It was only when they went 2-0 down that Hull started to press home their one-man advantage, but Marney and Bryan Hughes both failed to make the most of opportunities that fell their way, while Kenny saved well from a Windass free-kick.
