James Beattie kept his cool to net his ninth of the season from the penalty spot as the Blades battled for a home point against Preston on Saturday.
The leading scorer drilled home from 12 yards with ten minutes remaining after Sean St Ledger was controversially adjudged to have handled in a challenge with substitute Danny Webber.
United trailed to Darren Carter's first half free-kick and despite the gallant fight back are still without a win a Championship win in six games.
Following the disappointing performance at Bristol City and the fortnight's break, boss Robson made a total of five changes with new loanee Bardsley among the starting XI.
Preston opted to kick towards their fans in the Bramall Lane stand in the first half and the travelling contingent were soon trying to influence the referee. The visitors won three successive corners around the five-minute mark and from the third there were two separate appeals for a penalty but Mr Singh decided that Armstrong had not handled and Carter was not fouled.
The Blades also won a number of early free-kicks and corners, including one in the 10th minute which Beattie flicked over.
From another corner, on 17 minutes, Cahill had an effort blocked and then shouts for a penalty waved away and both sides created half chances around the midway point. Carter fired over after Hawley headed down, whilst for United, Beattie met Bardsley's cross but was too far out to test Lonergan.
On 32 minutes Sedgwick turned outside Stephen Quinn and shot over before Preston took the lead with their next attack. Armstrong was fortunate to escape a booking following a foul on Jones 35-yards out but United were not so lucky moments later. CARTER's left-footed inswinger managed to elude a crowded box and curl past Kenny.
Alan Quinn delivered an interesting centre from the byline and Stead fired over from distance as United's response was to increase the tempo. Another corner before the interval saw Lonergan spill the ball and moments later the half-time whistle was greeted with applause for effort drowning out a minority of booing.
Preston were out early for the second half and went through a special warm-up routine before the action recommenced. United, meanwhile, threw on two strikers at the break - Shelton and Webber - which indicated a change in formation.
The two substitutes were quickly into the thick of things and were involved in a build up on 47 minutes which resulted in Alan Quinn's shot being deflected wide.
Lonergan clawed out a deep Gillespie cross which Beattie fancied and then the Preston goalkeeper made a tremendous save, although how much he knew about it only he will be able to say. With 61 minutes gone, Preston half-cleared a Blades move but Bardsley powered forward to drill a 30-yard effort at goal, only for Lonergan to direct the ball over the crossbar.
Quinn's half-volley flew straight into Lonergan's arms moments later, whilst the crowd began to get anxious as Preston attempted to slow down proceedings.
Shelton's pace, effort and neat touches were causing problems for the Preston defence, who were backing off and paid the price as the game entered the closing stages.
From Tonge's ball down the left channel, Webber challenged with St Ledger and the Blades striker immediately appealed for a penalty. Referee Singh looked disinterested but then amazed the visitors by pointing to the spot.
North End's protests fell on deaf ears and BEATTIE waited patiently before sending the goalkeeper the wrong way with the subsequent penalty. United celebrated and ahead of the action restarting, Preston boss Simpson was sent to the stands, presumably for words spoken out of turn to the fourth official.
The incident caused friction between both sides and the booking count went up to six as injury-time approached.
From Gillespie's cross, Hill's headed clearance fell to Shelton who forced a near post save out of Lonergan whilst the fourth extra minutes added failed to separate the teams, although United had another appeal for a penalty when St Ledger and Webber clashed yet again.
Blades: Kenny, Naysmith, Bardsley, Beattie, Stead (Shelton 45), A. Quinn (Tonge 76), Kilgallon, Gillespie, Armstrong, Cahill, S. Quinn (Webber 45).
Unused: Morgan, Sharp.
Preston: Lonergan, Davidson, Mawene, Sedgwick, Hawley, Gallagher (Agyemang 66), Carter (Whaley 84), Chilvers (St Ledger 20), Hill, Jones, Nicholls.
Unused: Neal, Mellor.
