Chelsea's defensive and set-piece woes continued under Xabi Alonso as Brentford claimed an emphatic 3-0 victory in the west London derby.
It was all too easy for Brentford to win it as first Mikkel Damsgaard's corner was nodded across by Jannik Schuster, leaving Jaidon Anthony to nod home unmarked from a few yards out.
Then with Chelsea pushing for a leveller and moving to a back four, Brentford hit the Blues on the counter as Kevin Schade broke through. His one-on-one was saved by Emiliano Martinez but Igor Thiago struck home from close range to end his seven-game goal drought.
And with virtually the last kick of the game, Fabio Carvalho scored his first Premier League goal since his near-year-long injury lay-off after tucking home Schade's cross while unmarked at the far post.
Chelsea have now conceded 12 goals - the most in the league - from five Premier League games as the wait for their first top-flight clean sheet of the season goes on.
Unimpressive in defence, but in attack, Chelsea weren't much better - clearly missing the injured Joao Pedro, with replacement Danny Welbeck failing to generate any clear chances in his place.
Moises Caicedo was another big miss, with his replacement being Jordan Henderson, who made an unsuccessful first start for the Blues at the club he joined them from.
Cole Palmer looked bright in sparks, but the Blues never really generated anything apart from Pedro Neto's ninth-minute effort, kept out by Caoimhin Kelleher.
Brentford - who have become the first team to stop Chelsea scoring this season - continue their unbeaten start to the season to go up to third. Speaking of three, that's the number of Premier League games without a win for Alonso's Chelsea.
9: SAVE! Danny Welbeck tees up Pedro Neto in the area but his shot is saved by Caoimhin Kelleher.
41: BLOCK! Morgan Rogers has a good shooting chance in the penalty area but his effort is blocked by Schuster.
50: OFF THE BAR! Anthony strikes the top of the bar with a header from inside the box. The offside flag goes up but replays showed he was level.
61: GOAL! Brentford take the advantage as Schuster heads Mikkel Damsgaard's corner across and Anthony nods in from a few yards out.
82: GOAL! Schade breaks through for a one-on-one but sees an effort saved, yet Thiago taps in the rebound to seal the points.
90+4: GOAL! Carvalho makes it three by tapping home at the far post from Schade's wicked ball across.
Chelsea boss Xabi Alonso speaking to Your Site:
"I'm disappointed with the second half and with the result. This is not enough to compete in the Premier League.
"We were not able to maintain our level for the full 90 minutes and that's why we were punished today.
"It's about everything. It's about the mentality, the football and the tactical things that we need to keep improving. We can do much better."
On whether Joao Pedro's absence played a part:
"It's not about looking for excuses.
"We need to look at each other and know that we have to work and improve because there is still a long way to go. We have to check many things.
"We got into situations, but we were not precise enough with the final action. That's why we didn't score."
Brentford boss Keith Andrews speaking to Your Site:
"I think it's important that you enjoy these nights. There's no point hiding it. There are some tough days in the game, and you've got to enjoy the different emotions.
"I felt like there was something bubbling towards tonight. I have this unbelievable calm around the team because I trust them, so it's nice to see it come to fruition.
"I see humility and hunger within the group every day. We're very respectful of each other, but we're going to get better. We have to continue improving in this league.
"We try to push boundaries and be really open with each other. Let's continue on our journey because I'm loving it."
