Joao Felix became the first player to be sent off for Chelsea on their Premier League debut as Fulham piled more misery on Graham Potter's side with a 2-1 win over their West London rivals at Craven Cottage.
Carlos Vinicius’ header earned the hosts their fourth straight top flight win for the first time since 1966.
Both teams started brightly, with Vinicius and Felix firing off-target at either end, before Bobby Decordova-Reid rattled the bar for the hosts. Minutes later, the Cottagers took the lead as the Blues failed to deal with a cross into the box which fell to Willian, who saw his deflected shot beat Kepa.
The visitors desperately tried to get back into the game before the break, but they were twice thwarted by Bernd Leno, who firstly made a brilliant stop from Lewis Hall’s effort, which took a clip off a defender, before making a smart stop from Felix’s snapshot.
Chelsea’s fortunes were somewhat better after the break though as they equalised just two minutes into the second period through Kalidou Koulibaly, forcing home from close range after Mason Mount’s free-kick had rattled the post.
That was as good as it got for the Blues though, who had Felix sent off just before the hour mark, receiving a straight red card for a reckless and high tackle on Kenny Tete.
15 minutes later, Fulham retook the lead thanks to Vinicius’ towering header, meeting Andreas Pereira’s cross to nod home and earn Marco Silva’s side a thoroughly deserved three points, while Chelsea suffered their sixth defeat in eight games.