Yeovil Town pulled off a smash and grab raid at Griffin Park as they recorded a 2-1 win.
Brentford dominated the match but conceded the opening goal only for Charlie MacDonald to level it up.
But Richard Lee was sent off for Brentford for an offence not entirely clear to the Griffin Park crowd and Paul Wotton lashed in a winner for The Glovers.
Brentford started much the brighter and had the better of the opening 20 minutes.
The home side were full of attacking intent and looked likely to open Yeovil up, particularly through the interplay of Michael Spillane, Robbie Simpson and Gary Alexander.
They probably didn't create as many early chances as their possession indicated they could but Yeovil had to be alert to block an Alexander shot and Myles Weston couldn't fire in the re-bound.
Simpson shot wide at the near post for The Bees before the home side had a spell around the 20-minute mark where it seemed inconceivable they would not score.
Kevin O'Connor curled in a corner, Owain Tudur Jones and Karleigh Osborne miss-hit volleys and the ball fell to Simpson who saw hit toe-poked effort cleared off the line.
The ball came back in, Weston nodded down and got the return from MacDonald before a low shot forced Stephen Henderson into a low save and the Yeovil stopper scrambled the ball behind as Simpson waited.
From the resulting corner, Tudur Jones' header was saved superbly by Henderson, who got up quickly to block the re-bound from Alexander.
And those series of saves in the space of 90 seconds proved particularly valuable when Yeovil took the lead seconds later, just about the first time they entered Brentford territory.
The home side failed to deal with one of Henderson's long punts up field and Andrew Williams got in past Lee, Osborne was able to clear off the line but the ball fell to Oli Johnson, Osborne reacted again to deny him once but could do nothing as the nippy striker poked in.
Still Brentford held the upper hand, Paul Huntington's sliced clearance from a drilled O'Connor cross fell fortunately for Henderson and the goalkeeper somehow kept out a low MacDonald shot with his legs.
The visitors were reliant on pace in attack and long balls in behind to pose an attacking threat, and they were dangerous on the break but Wotton lashing a shot miles off target was their only other attempt on goal in the first 44 minutes apart from Johnson's opener.
The home side did not deserve to be behind, and worked their way level late in the first half.
A quick free kick was worked to Osborne, he fed MacDonald on the edge of the box and the striker turned and lifted a superb shot over Henderson and into the net from the edge of the box.
Lee had to be alert to keep out an Andrew Williams shot on a rare Yeovil attack in the dying seconds of the first half and Ed Upson lashed the re-bound well wide.
Brentford started the second half as they played most of the first, on the front foot and in the ascendency.
MacDonald forced a low save from Henderson after good work from Tudur Jones, Simpson and Alexander and Craig Woodman fired narrowly wide after a marauding run up forward.
Henderson was in action again to deny Alexander after the striker turned well on the edge of the box and MacDonald lifted an effort wide after picking up a Woodman pass.
The game became more even as the second half wore on, albeit Yeovil couldn't create many openings and Brentford had more attacking intent.
Brentford came within a whisker of taking the lead when Woodman threw the ball in and MacDonald nodded into the path of substitute Lewis Grabban, the new signing fed Alexander and he whistled a shot inches past the post after a sharp turn.
Henderson saved a MacDonald shot when he reached a Simpson pass and Spillane looped a header on to the roof of the net while Dean Bowditch lifted an effort well over with Yeovil's first attempt of the second period half an hour in to it.
Alexander flicked a header from a Grabban cross narrowly wide before the game swung Yeovil's way in bizarre circumstances.
Osborne failed to get sufficient distance on a back header and Lee came out to challenge Andrew Williams - the Brentford goalkeeper appeared to get the ball but referee Peter Quinn, who had made a number of decisions that surprised and infuriated both sets of players, deemed he had committed an offence, although exactly what was unclear.
If the game had been allowed to continue Yeovil would have led as the ball was floated into the back of the net from 50 yards but instead, Lee was dismissed and Simon Royce was brought on for his Brentford début in place in Simpson.
His first task was the pick the ball out of the back of his net as the free kick was worked to Wotton and he lashed in.
O'Connor fired a free kick into the defensive wall as Brentford sought an equaliser but, with the extra man, Yeovil saw it through to take the win.
Brentford: Lee; Spillane (sub Forster 85 mins), Osborne, Balkestein, Woodman; Simpson (sub Royce 83 mins), O'Connor, Tudur Jones, Weston (sub Grabban 62 mins); MacDonald, Alexander
Subs (not used): Wright, Legge, Laird, Diagouraga
Bookings: Alexander (43 mins) (third of season), Spillane (64 mins) (fifth of season), Woodman (71 mins) (fifth of season)
Sent Off: Lee (83 mins)
Yeovil Town: Henderson; Kalala, Ehmer, Huntington, Smith; Welsh (sub S. Williams 82 mins), Upson (sub Russell 58 mins), Wotton, Bowditch; Johnson; A. Williams
Subs (not used): Martin, Jones, Calver, Gibson
Bookings: Johnson (23 mins), Kalala (77 mins), Wotton (79 mins)
Attendance: 4,753 (285 away fans)
By Chris Wickham