The Blades goal came when Michael Tonge worked hard on left hand side where his cross was eventually headed home by Graham Alexander, the cross was intended for Carl Asaba.
The opposition went quickly down to ten men when Mark Rankine was sent off for foul and abusive language after the referee turned down the penalty when ex-Wednesday striker Richard Cresswell was brought down by Shaun Murphy.
The visitors had been keeping in-form United at bay, with goalkeeper David Lucas looking unbeatable between the posts.
He first showed his mettle when England Under-20 star Tonge was fouled by Tyrone Mears just outside the box and got up to strike a superb free-kick that produced a great save by the keeper.
Lucas then did superbly well to save a long-range effort from Peter Ndlovu as United - on a high after their midweek Worthington Cup heroics - went in search of a breakthrough.
The overworked keeper also had to be at his best to tip a header
from Steve Kabba round the post after the striker got on the end of Jon Harley's cross from the left.
As the first half drew to a close Cresswell struck a shot wide of Paddy Kenny's post in a rare Preston attack.
Blades boss Neil Warnock opted for more teeth in the second half, sending on leading scorer Asaba as a third striker in place of midfielder Nick Montgomery.
His side were soon on top again and Lucas was called into action to save a shot from Kabba before the drama of the own goal and sending-off.
United, trying to make it nine games unbeaten in all competitions, were soon going for the jugular, Harley firing in a long-range free-kick that Lucas saved and defender Shaun Murphy heading wide from a corner.
Warnock called midweek two-goal hero Paul Peschisolido into the fray for the last 12 minutes, but it was Preston, searching for the goal that would have given them a share of the points for the 11th time this season, who went closest.
Leading scorer Cresswell got in a header that Kenny did well to tip round the post, and there was no way back for the visitors.