Chelsea’s unbeaten run survived, but their grip on victory slipped away as Brentford struck deep into stoppage time for a 2-2 draw at the Gtech Community Stadium.
Kevin Schade’s deflected first-half finish gave the hosts the lead, with the Blues struggling for rhythm until Cole Palmer came off the bench to level midway through the second half.
Moisés Caicedo then looked to have sealed all three points when he rifled home five minutes from time after Alejandro Garnacho’s lively debut run sparked chaos in the box.
But Brentford refused to lie down, and in the 94th minute Fabio Carvalho pounced at the back post from Schade’s long throw to send the home crowd wild and deny Chelsea top spot in the Premier League.
Enzo Maresca’s side will take little comfort from remaining unbeaten as they turn to Bayern Munich in the Champions League on Wednesday, while Brentford will celebrate their resilience in life after Thomas Frank.