The Blades looked to be heading for a comfortable win after Neil Shipperley's first-half strike and Paul Ifill's effort early in the second period.
However, Taylor brought on Stuart Elliott and Darryl Duffy and the pair made an instant impact.
Elliott pulled a goal back just after the hour mark before Duffy deservedly levelled with 11 minutes remaining.
But Unsworth sent the points United's way after he finally broke Boaz Myhill's resolve to smash the ball home.
The Tigers all but ensured they will be playing Coca-Cola Championship football again next season after embarking on an impressive four-game unbeaten run which had included three victories, culminating in a confidence-building success over promotion hopefuls Leeds last weekend.
The Blades, meanwhile, are on the verge of securing promotion to the Barclays Premiership after a top-flight absence of 12 years and this Yorkshire derby came less than two weeks before they entertain Kevin Blackwell's Leeds.
United were also able to call upon the same starting XI that drew with Stoke last weekend.
For Hull Alan Rogers and John Welsh both failed to make the game after struggling with illness this week so Andy Dawson and Billy Paynter stepped in.
Hull started strongly and they first threatened after six minutes. A poor clearance from the Blades landed at the feet of Keith Andrews who sent his shot just wide from 25 yards.
Unsworth's clinical free-kick soon after was the Blades' first effort on goal but 'keeper Myhill pushed the ball away to safety.
The Tigers' best chances were arising through shots from distance and again United goalkeeper Paddy Kenny had to be alert to palm away a stinging effort from Kevin Ellison.
But United found their feet midway through the half and should have taken the lead through Phil Jagielka.
Leon Cort fluffed his attempted clearance from a low cross and the ball fell to the Blades' player of the year who swept a shot on goal but Myhill somehow caught the ball between his legs.
The Blades continued to get sharper as the half wore on and they made their pressure tell in the 36th minute.
Despite the attention of the visitors' defence, Michael Tonge crossed into the box and Shipperley got the better of his marker to poke the ball into the back of the net for his 11th goal of the season.
Seven minutes into the second half United scored their second.
With his quick feet causing problems, Danny Webber worked himself some space down the left wing to send an inch-perfect cross to Ifill who headed strongly beyond Myhill.
But some poor defending by the Blades let Hull back into the game just after the hour mark.
A cross from Alton Thelwell found substitute Elliott in space and he smashed the ball high into the back of the net to give the visitors hope.
Soon after Hull were controversially denied a penalty but they were not to be denied in the 69th minute.
Stuart Green crossed into the box and, as the ball eluded the United defence, substitute Duffy stabbed beyond Kenny.
Elliott headed tamely wide when presented with an open goal while Webber headed just over when it seemed easier to score.
Unsworth rattled the bottom of the post in the dying moments but, with seconds remaining, the defender swept home the winner.