Boro had to play with a weakened team after a Covid-19 outbreak but drew level after Sam Folarin canceled out Halil Dervisoglu's first-half opener. Saman Ghoddos then scored the winner as the Bees progressed to the fourth round.
Our Boro writer Joe Nicholson has dished out his marks from the match – scroll down and flick through the pages to see them:
5. Hayden Coulson - 6
Struggled early on and lost his man for the goal. Man marked Halil Dervisoglu even when the Brentford winger cut inside. 6 Photo: Clive Brunskill
6. Hayden Hackney - 6
Looked good on the ball but dropped to deep in midfield at times. 6 Photo: JPI Media
7. Lewis Wing - 6
Tested the keeper with a powerful free-kick in the first half. Made a sloppy pass which almost led to a goal in the first half but tracked back to help his defenders when he needed to. 6 Photo: Alex Burstow
8. Marcus Browne - 7
Warnock says Marcus Browne's knee cap went out and back in. They are hopeful it isn't as bad as first feared. 7 Photo: Alex Burstow