This goal-less draw was not without incident.
During the first half referee Eddie Ilderton awarded Brentford a penalty and sent off Kieron Freeman but moments later changed his mind and reversed both decisions.
United battled hard against second-placed Brentford and were full value for at least a point.
McGinn and Paynter started, they were straight replacements for Scougall and Baxter, who dropped to the bench after picking up minor injury problems at the weekend. In the absence of the suspended Maguire, Brayford continued in central defence.
Brayford and co were busy for the opening 15 minutes as Brentford, undoubtedly, made the brighter start. Inside 30 seconds Donaldson shot at the goalkeeper and following a sliced clearance by Howard, Trotta's shot deflected off Brayford before Freeman cleared. In addition, Donaldson headed wide a corner and the same striker lashed over after a fortunate ricochet put him in the clear.
United's early action centred around Murphy on the left. There was an unsuccessful appeal for a penalty when the Murphy was felled by McCormack and then the winger provided a cross which Coady almost attached himself to.
In an entertaining start, Howard punched out Forshaw's corner but Diagouraga smashed back with a volley which was just wide and then, on 24 minutes, the Blades fans were on their feet. Flynn released Coady and after drawing the goalkeeper out of position, his low cross for Murphy was cut out at the decisive moment by Tarkowski.
Then the controversy started, just after the half hour mark. Freeman, looking to atone for an error, managed to get a toe on the ball to prevent Trotta bearing down on Howard. The Kop applauded as he was successful but referee Ilderton disagreed, pointed to the penalty spot and showed his red card to Freeman. Unitedites were in disbelief, the players asked the official to speak to one of his assistants and after a lengthy discussion the decision was altered. Freeman stayed on and play was restarted by a dropball, after protests from Brentford.
That delay, plus an injury to Paynter, ensured five minutes of added time was played but the only notable action in the remainder of the half was a booking for McCormack for a crude foul on Murphy, and the half-time discussions, unsurprisingly, were about the Freeman incident.
Like the end of the first half, the start of the second was quiet, although Brentford were the more prominent, Freeman did well to block a shot from Diagouraga on 57 minutes.
Porter replaced Paynter just before the hour and immediately caused problems for Bees goalkeeper Button in an aerial challenge, whilst Flynn curled over soon after.
A long-range effort from Douglas moved in the air but was collected by Howard, whilst the Blades were now causing problems for the visitors. Coady's effort was blocked by Diagouraga after a short corner and from another set-piece Porter headed over.
Goalkeeper Button adopted a safety-first policy when tipping over a looping Porter header and boss Clough replaced a midfielder with a striker when Baxter took over from McGinn in the final ten minutes.
Trotta went close following a break but the Blades were asking the questions late on and Flynn's curler was touched wide by Button.
Dallas fired wide in a frantic end and Trotta beat two players but fired at Howard as the tension grew. Four added minutes was announced as Davies picked up United's first booking and Kennedy took over from Flynn but there was no further goalmouth action as both sides had to settle for point.
Blades: Howard, Brayford, Flynn (Kennedy 90), Doyle, McGinn (Baxter 83), Collins, Coady, Paynter (Porter 59), Davies, Murphy, Freeman.
Unused: Scougall, Long, Khan, Dimaio.
Brentford: Button, Forshaw, Craig, Douglas, Donaldson, McCormack, Judge (Dallas 79), Diagouraga (Saville 71), Bidwell, Tarkowski, Trotta.
Unused: Lee, Dean, Grigg, Reeves, Yennaris.