Brentford defeated Chelsea 2-0 at Stamford Bridge on Wednesday to win the Premier League, making it Chelsea's sixth consecutive defeat since Frank Lampard was named temporary manager.
Cesar Azpilicueta's own goal gave the visitors the lead in the first half, and substitute Bryan Mbeumo added a second by running unopposed the length of the field to smash home a finish and extend Chelsea's losing streak at home to six games overall.
In its previous seven games, Chelsea has only managed one goal and has gone winless.
Chelsea will have had four different managers since its last win if, as is becoming more and more likely, Mauricio Pochettino is named the team's long-term replacement for Graham Potter by the time Chelsea faces Arsenal on Tuesday.
Chelsea may now struggle even to finish in the top half of the Premier League after falling six points behind Fulham in tenth place.
“This club has experienced many, many good moments recently, and this moment is tough,” said Lampard, who, since being reinstated as manager on an interim basis, has seen his team lose three Premier League games and twice in the Champions League against Real Madrid. “We'd love a magic wand and a magical moment, but in football that doesn't happen because the Premier League is so competitive. We have to struggle to get our chance.
“The same thing applies; keep going and keep working. When a team is used to winning often, this point in the season is difficult.
Chelsea got off to a slow start and only got worse. After a deft first-time pass from Conor Gallagher, Ben Chilwell's strong left-side surge during the first half may have been the lone moment of expectation at Stamford Bridge.
The only indication of offensive intent from either side throughout the first 20 minutes was Chilwell's low cross, which was blocked.
As Chelsea looked for a way through, N'Golo Kante arrived on the right touchline, bending over an appealing cross. Thiago Silva got his head to the ball up and free within the box, but his effort lacked force and only connected with David Raya's palms.
On the half-hour mark, Kante controlled the ball inside the box after Wesley Fofana's cut-back and passed it to Enzo Fernandez, posing the first real challenge for the Brentford goalkeeper. The World Cup champion fired too close for Raya, who deflected it behind. He has yet to score since his record-breaking transfer to Stamford Bridge.
Mathias Jorgensen flicked Mathias Jensen's corner, and Azpilicueta had little time to react as the ball bounced past Kepa Arrizabalaga and off the Chelsea captain.
After being shut out by many managers, Pierre-Emerick Aubameyang came off the bench for the second half. His entrance seemed to give Chelsea's onslaught some energy.
Soon after the restart, Kante attempted an angle shot that went just wide, and then Aubameyang used fantastic movement to create space for a shot that went straight at Raya.
Mbeumo scooped up the ball and moved into the area for the second goal while still barely inside the Chelsea half. Mbeumo buried Chelsea by smashing the ball with his left foot inside the near post.
As home supporters rushed out of the stadium, the ecstatic away support sang, “West London is ours.”
The specifics of the game are rather obvious, according to Lampard. “At the top of the pitch, we lack confidence. Even though this is not a sad tale, everything is working against us. Even though we didn't generate many huge opportunities, we were always in control, so that game was obvious.
