A late goal from substitute Ryan Brunt condemned Brentford to a London derby defeat against Leyton Orient.
Brentford had more chances than their hosts and restricted the East London side but were punished when they failed to clear a long throw.
Orient were rewarded for finding a way to keep Brentford out and then took their chance when it came.
Brentford created plenty of chances in the first 45 minutes but were unable to get themselves ahead.
Orient goalkeeper Ryan Allsop kept out a low Harry Forrester free kick and held on to a lofted effort from the same man soon after.
Clayton Donaldson failed to get enough power on a lob when he latched on to a Shaleum Logan pass and Allsop saved before the Brentford striker stung the palms of the goalkeeper with a fierce shot and then had a header blocked.
Orient had barely been in the game in the first quarter – Logan blocked a low Lee Cook shot – but Jonathan Douglas was forced in to a block when a free kick fell to Michael Symes inside the six-yard box.
For a ten minute period just past the half hour, Brentford were imperious.
They barely let the hosts have a kick, but they still couldn’t score.
Forrester had a shot blocked and then, from a similar position in the right channel, forced Allsop in to a low save.
Toumani Diagouraga shot wide, Adam Forshaw lifted a lob narrowly over and Tony Craig missed the target with a header as Brentford pressed.
The best chance fell to Paul Hayes after Forshaw and Logan combined on the right but Ben Chorley appeared to make a block when the Brentford striker looked set to finish from eight yards.
Cook lifted a free kick just past the far post as time ran out in the first period and Forshaw shot wide in stoppage time.
The game opened up a bit more after the break – Brentford still held the upper hand in the early stages but Orient put a few more men forward to create chances of their own.
Harlee Dean lashed over when a corner dropped in the box and Nathan Clarke made a block when Hayes tried to turn in a Forrester cross following a nice break.
Craig blocked a Kevin Lisbie shot when Orient put an attack together while at the other end a Jonathan Douglas free kick was deflected wide and Craig headed the resulting corner over.
The game became more stretched as it entered the final 25 minutes but most of the chances fell to the visitors.
A Jake Bidwell free kick was flicked narrowly over his own bar by Chorley, Forrester had a shot blocked and a deflected Hayes effort flew wide with Allsop stranded.
Anthony Griffith shot wide for the hosts and a Bidwell free kick was saved high to his left by Allsop.
Martin Rowlands turned a Lisbie cross wide while at the other end a Douglas volley was deflected wide and Allsop held a Dean header.
Brentford looked like they had complete control but were hit by a sucker punch.
A long throw wasn’t cleared, Rowlands lifted it back in and Brunt toe-poked the ball home as Brentford were unable to get it away.
The Bees were unable to find an immediate response and Orient could have doubled their lead – Simon Moore saved a Dean Cox shot and Lisbie headed wide.
The visitors did press late on but the Orient defence stood firm.
A Douglas shot was deflected wide and Allsop kept out a low Donaldson effort.
Substitute Farid El Alagui headed a Logan cross wide and then lashed a shot wide from a tight angle.
Eventually time ran out for Brentford and Orient took the points.
Leyton Orient: Allsop; McSweeney, Chorley, Clarke, Sawyer; Cox, Griffith, Rowlands (sub Smith 85 mins), Cook (sub Odubajo 75 mins); Lisbie, Symes (sub Brunt 62 mins)
Subs (not used): Grainger, Baudry, Laird, Mooney
Bookings: Rowlands (57 mins), Cook (73 mins)
Brentford: Moore; Logan, Dean, Craig, Bidwell; Forshaw (sub Adeyemi 74 mins), Douglas, Diagouraga, Forrester (sub Saunders 80 mins); Hayes (sub El Alagui 80 mins), Donaldson
Subs (not used): Gounet, Legge, Barron, O’Connor
Bookings: Craig (40 mins), Bidwell (80 mins)
Attendance: 3,333 (508 Bees fans)
By Chris Wickham