Chelsea slumped to a miserable fifth successive defeat under Frank Lampard as Brentford again claimed west London bragging rights at Stamford Bridge.
An unfortunate first-half own goal from returning captain Cesar Azpilicueta and a late breakaway effort from substitute Bryan Mbeumo sealed more derby success for the resolute Bees, who ended a six-match winless run to provide a boost to their previously fast-fading European hopes despite only having one shot on target all night.
But for troubled Chelsea, yet another loss deepens the sense of chaos around the club as a truly miserable season continues to hit new lows, piling more pressure on interim boss Lampard as former Tottenham boss Mauricio Pochettino is lined up to take over in future.
After waiting 85 years for a win on enemy territory at the Bridge, Brentford now have two in as many seasons after a memorable 4-1 romp in SW6 12 months ago.
They jump above another local rival in Fulham up to ninth, six points off the top six with five matches left to play this term. Chelsea, meanwhile, stay hopelessly marooned in 11th, almost closer to the foot of the table than to Liverpool in sixth spot after another harrowing night.
They are on course to finish behind both Fulham and Brentford for the first time in the Premier League era and have now gone nine games in total without a win across all competitions.
Lampard sticking with a defensive 3-5-2 system with midfielder Conor Gallagher up front alongside Raheem Sterling, deputising for injured top scorer Kai Havertz, proved costly, with a familiar lack of forward threat and end product in the first half.
Brentford, who showed four changes from their improved draw with in-form Aston Villa on Saturday, went ahead in fortuitous circumstances, when a corner conceded by Azpilicueta - making his first appearance for more than two months in place of Reece James, who, along with Mason Mount, has now been ruled out for the season - unwittingly deflected in off his arm after a near-post flick-on.
Chelsea, loudly booed off at half-time, got a much-needed response after sending on Mykhailo Mudryk and Pierre-Emerick Aubameyang at the interval and switching to an attacking 4-3-3 formation, placing their opponents under constant pressure for around 20 minutes and fashioning several good chances as they looked far more threatening with genuine width and a focal point up front.
However, Brentford continued to defend stoically as Chelsea ran out of steam and countered to secure another terrific derby triumph with their only shot on target of the evening, sub Mbeumo leading the charge, cutting inside and beating Wesley Fofana before his strike deflected off the heel of Thiago Silva and beat Kepa Arrizabalaga at his near post.
Home fans quickly streamed for the exits on another harrowing night, with those that remained leaving Lampard and the players under no illusions as to their unhappiness with a season that has long since spiralled out of control.
