A debut goal from new loan signing Dean Bowditch was not enough to prevent Brentford slipping to their first home defeat of the season.
Visitors Rochdale struck twice in the last quarter of an hour of the first half to take a lead they were able to hold on to despite lots of second half pressure from the home side.
In terrible conditions Rochdale were able to play some nice football, particularly after Rory McArdle had given them the lead, but they ended up hanging on in the later stages as Brentford pressed for an equaliser.
The game had been pretty even in the early stages; Glenn Poole had shot narrowly wide for Brentford and then sliced an effort while Chris Dagnall forced Ben Hamer into a save at the other end.
Will Buckley fired wide for Rochdale after a nice run and Dagnall headed over while Charlie MacDonald forced Sam Russell into a low save at the other end after linking well with Bowditch.
Rochdale took control of the game just past the half hour when McArdle rose unchallenged to head a Tom Kennedy corner in from ten yards out and the visitors could have put Brentford out of it completely in the next 15 minutes.
Hamer saved from Adam Rundle and Dagnall had a shot blocked before Buckley doubled the lead when he latched onto a Lee Thorpe nod down, skipped past James Wilson and steered a shot past Hamer into the far corner, although it did look like he had used his hand in the build up.
Ciaran Toner had a low cross-cum-shot blocked late in the half before Kevin O'Connor shot over just before the whistle.
The half time introduction of Ryan Dickson and Mark Phillips reinvigorated Brentford, Poole fired wide at the near post seconds into the half and within five minutes Brentford had a lifeline.
Rochdale failed to clear a free kick and Poole skipped to the by-line, he dug out a cross to the far post where Bowditch headed in.
Brentford continued to press, Alan Bennett headed a Poole corner wide and Russell managed to save when it looked as if the home side were going to scramble an equaliser when Bowditch and Marcus Bean had shots blocked.
Kennedy had a shot blocked, McArdle had a header deflected wide and Thorpe headed over for the visitors but it was Brentford doing most of the pressing.
Phillips forced a flying save from Russell with a shot from the touchline, Bennett headed wide and Marvin Williams shot off target as The Bees searched for an equaliser.
They had a couple of decent appeals for penalties turned down but the goal would not come and Brentford trudged off defeated at Griffin Park for the first time since April.
Brentford: Hamer; Newton (sub Phillips h/t), Wilson, Bennett, Wood (sub Dickson h/t); Williams, O'Connor, Bean, Poole; Bowditch, MacDonald
Subs (not used): Brown, Pead, Halls
Rochdale: Russell; Wiseman, McArdle, Stanton, Kennedy; Buckley (sub Thompson 89 mins), Toner, Jones, Rundle, Thorpe, Dagnall (sub Le Fondre 63 mins)
Subs (not used): Spencer, Keltie, Holness
Attendance: 4,291 (292 away fans)
Written by Chris Wickham