First-half goals from Bees new boys Robbie Simpson and Craig Woodman gave the hosts the lead against their bogey side at Griffin Park on Tuesday night before Sean Jeffers reduced the arrears on the hour mark.
Brentford hit the bar twice in the opening stages through defenders Karleigh Osborne and Leon Legge, before Huddersfield loan man Simpson made the breakthrough from Woodman’s cross after 31 minutes.
Woodman stretched the lead four minutes later with a free-kick over the wall that gave keeper Scott Brown no chance.
But if Brentford dominated before the break the Robins were rampant after it and made Andy Scott’s side sweat for their first normal-time League Cup win in four years.
A long-range free-kick on 61 minutes saw the Bees defence stand still after keeper Simon Moore parried and on loan Coventry striker Jeffers was quickest to react and slam home the rebound.