Chelsea dominated first-half proceedings and could’ve been ahead on 10 minutes as Noni Madueke’s curling effort hit the crossbar.
Cole Palmer was pulling the strings in a central attacking midfield role, first crossing for Marc Cucurella - who has never scored for the Blues - but the Spaniard’s tame shot was comfortably saved by Mark Flekken.
Palmer then set up Raheem Sterling moments later, but he skewed his effort over. Brentford’s best chance of the half fell to Bryan Mbuemo, whose cross-come-shot was saved by Robert Sánchez.
The second half opened with a strange incident involving Neal Maupay, who as a substitute, was booked for coming onto the pitch and kicking the ball away before Palmer was about to take a free-kick.
Just a couple of minutes later, Brentford went ahead, as Mbuemo’s cross found Ethan Pinnock at the back post, who headed his first goal this season into the back of the net.
Chelsea assistant manager Jesús Pérez was sent off late on, while the Bees almost doubled their lead on the counter-attack, as Sánchez saved well before Mbuemo fired wide.
Deep into stoppage time, Sánchez came up for a corner and couldn’t get back in time, allowing Mbeumo to finally get his goal as he tapped into an empty net.
A disappointing defeat means Chelsea have now only won one of their last 13 Premier League home games.
Meanwhile, Thomas Frank’s Brentford leapfrog them into the top half of the table after securing back-to-back victories following a six-match winless league run.
Flashscore Man of the Match: Bryan Mbuemo (Brentford)
