Chelsea's revival came to a grinding halt in a 2-0 West London derby defeat to Brentford, who have become the first-ever visiting team to win each of their opening three Premier League games at Stamford Bridge.
Mauricio Pochettino's team dominated the possession and shot counters, but Thomas Frank's side defended admirably and drew first blood through Ethan Pinnock's powerful header, before Bryan Mbeumo doubled the Bees' tally with seconds remaining, making the Blues pay for their worrying profligacy.
With neither Enzo Fernandez nor Mykhaylo Mudryk making the hosts' squad due to fresh knocks, the door swung open for Noni Madueke to make his first Premier League start, and the ex-PSV Eindhoven man almost justified Pochettino's decision with just 10 minutes gone.
While both sides enjoyed forays forward in the earliest exchanges, Chelsea countered with pace after every Brentford set piece, one of which ended with Madueke cutting in from the right and curling a sumptuous strike onto the bar with 10 minutes gone.
Pochettino's side continued to make inroads at will, as Mark Flekken got down to his right to beat away a Conor Gallagher drive in the 12th minute, before Cole Palmer picked out the run of Marc Cucurella with a delightful inswinging delivery in the 19th minute, but the Spaniard's tame volley landed straight into the arms of the Bees goalkeeper.
Brentford's besieged defence continued to hold out, although Mads Roerslev was arguably fortunate not to give away a penalty for a shove on Raheem Sterling in the 24th minute, which neither Simon Hooper nor VAR official Craig Pawson deemed spot-kick worthy.
For all of Chelsea's first-half dominance, Robert Sanchez was forced into the first meaningful action of the second half, as Mathias Jensen's cutback into the penalty area landed at the feet of Vitaly Janelt in the 50th minute, but the German could only shoot straight at the Blues goalkeeper.
However, the hosts' early profligacy would eventually come back to haunt them, as with 58 minutes gone, Mbeumo lifted an inviting delivery to the back post, where Pinnock surged beyond a jumbled Chelsea defence and directed a bullet header past a stranded Sanchez.
The same old story befell Chelsea as the Blues searched for an equaliser, with Pochettino's men stringing together several slick passing sequences in and around the Brentford box before a mishit final ball killed the attack, although the visitors' defensive masterclass more than played its part too.
Chelsea frustrations soon boiled over on the sidelines, as Pochettino's assistant Jesus Perez was given a red card - seemingly for something he said towards the Brentford dugout - and his dismissal would only mark the beginning of a chaotic 90th minute.
As Chelsea failed to make the most of a set-piece again, Brentford launched a four-on-one counter-attack, which ended with Sanchez bravely thwarting substitute Yegor Yarmolyuk before Mbeumo fired just wide of the post a few seconds later.
Sanchez then came up for a last-minute corner as Chelsea rolled the dice one last time, but the goalkeeper's risky endeavour backfired and then some, as Neal Maupay broke away on the counter-attack, shook off the backtracking Sanchez and slid in Mbeumo to tap home into an empty net.
Brentford and their ecstatic fans celebrated with a few Jurgen Klopp-esque fist pumps, as the Bees snapped their six-game winless run in all tournaments to rise to 10th in the table, leapfrogging Chelsea - who have only won one of their last 13 league home games - in the process.
The Bees have a week to recuperate before they tackle another London counterpart in West Ham United next Saturday, while Chelsea seek a spot in the EFL Cup fourth-round when they battle Blackburn Rovers on Wednesday.
