An improved second half display failed to prevent United slipping to defeat at a wet Griffin Park on Saturday.
Goals from Clayton Donaldson and Harry Forrester, both in the first half hour, secured Brentford's victory but home goalkeeper Simon Moore was in fine form and he was helped by two goal-line clearances.
Referee Andy D'Urso's final whistle signalled United's second consecutive away defeat.
Boss Wilson was boosted by the return of McMahon and Hill to the full-back positions, which left Westlake and Williams having to be content with places on the bench. There was further good news when Flynn and Miller shook off their calf problems to start in the capital... but there were very few smiling faces amongst the travelling contingent when the action got underway.
Just three minutes had elapsed when Brentford opened the scoring with their first attack. A slotted pass down the left channel disected the defence and found Diagouraga, whose low centre was turned in by DONALDSON, with the aid of Long's near post. Another break from Diagouraga caused further problems soon after.
United's first opportunity, on nine minutes, was close to levelling. From McMahon's deep cross, Flynn headed back into the danger area and Miller's nod towards goal was expertly tipped over by goalkeeper Moore. The Blades also won a couple of early corners but Long needed to be alert to deflect away another Bees threat, this time following a run by Trotta. The young goalkeeper was also called upon on 20 minutes to punch over a Forrester effort from distance and a Diagouraga header was wide from a corner.
The efforts were warnings as Brentford added a second just before the half hour. FORRESTER had already fired a shot at the back of one of his team-mates before picking the ball up in midfield and hammering past Long's right hand from 25-yards to double the home side's lead.
Forshaw was the next to fire in, hoping to use the slippery surface but he was off target and the final chance of the half fell to United but from McMahon's free-kick, Collins headed wide.
As the rain persisted, the Blades kicked towards the sold out away end in the second period and despite Long deflecting away a Forshaw shot away, the visitors did most of the probing in the early stages of the half.
Miller crept between two defenders to get on the end of a Porter flick but the subsequent shot was diverted by the onrushing Moore and then Porter fired into the sidenetting.
On the hour Blackman's shot after a run was parried away by Moore but the rebound evaded three Blades players and Wilson made two changes in quick succession, introducing Westlake and then Cresswell. Maguire was the next to go close, his header gathered next to the post by Moore from Blackman's corner and as the game entered the final 20 minutes, Blackman fired inches wide.
Brentford thought they had extended their lead on 78 minutes but were denied by a linesman's flag when Trotta tapped home after latching on to Long's parry from Dean's shot, whilst United's first booking was for Maguire's foul on Donaldson.
A clever dummy from Cresswell looked to have put Miller in the clear but he was denied by a last-ditch tackle from Bidwell and a Hill long-ranger was blocked. With four minutges remaining both Miller and Maguire were denied by clearances off the line and a McDonald shot looked goalbound before taking a deflection. The Blades thought a corner should have been awarded and Collins and McDonald were booked for protesting.
Five minutes of added time added a little hope but the only noteworthy action late on was Blackman being denied a penalty after being blocked off by Craig.
Brentford: Moore, Forshaw, Craig, Dean, Donaldson, Trotta (Hodson 81), Logan, Forrester, Diagouraga, Bidwell (Saunders 60), Kiernan (Hayes 67).
Unused: Lee, Barron, Dallas, Oyeleke.
Blades: Long, Maguire, Hill, Flynn, Doyle, Porter (Cresswell 65), Blackman, McDonald, Miller, Collins, McMahon (Westlake 61).
Unused: McAllister, Cofie, McFadzean, Williams, Coyne.