They needed penalties to beat Wycombe Wanderers in the EFL Cup after drawing 1-1.
Marcus Forss scored the winning spot-kick to make it 4-2 on pens to the Bees.
Brentford's reward is an away tie at Premier League Southampton in the next stage of the competition.
Crystal Palace will face Manchester City in the 3rd round, if they can beat Bournemouth in the 2nd.
And there's an all-top flight clash between Arsenal and Leicester.