Chelsea again lost a Premier League match as Ollie Watkins' fine strike gave Aston Villa a 1-0 win at Stamford Bridge on Sunday.
The Blues also saw a red card in the match as Malo Gusto was sent off after a crunching challenge on Lucas Digne.
Gusto's dismissal did prove to be Chelsea's undoing after they began brightly and had broken the deadlock through Axel Disasi moments before half-time, only for the goal to be chalked off for offside as Disasi mistimed his run from Raheem Sterling’s cross.
Watkins struck 15 minutes after the Blues were reduced to 10 players, firing home from the tightest of angles after a fine break with Moussa Diaby.
The defeat makes it Chelsea's worst start to a top-flight season after the opening six games since 1978-79.
Mauricio Pochettino's side are now languishing in 14th place with just five points this season, while Villa move into sixth, just two points off the top four.