Callum Wilson, Junior Stanislas and former Chelsea player Nathan Ake scored Bournemouth's goals at Stamford Bridge for possibly the most surprising result in the English Premier League this season.
It was Chelsea's first home loss in all competitions since September and the team's first loss in nine league games.
Chelsea manager Antonio Conte complained ahead of the game that preparation had been affected by the uncertainty surrounding striker Michy Batshuayi, who ended up leaving the club hours before kick-off to join Borussia Dortmund.
Olivier Giroud was signed from Arsenal in his place, but wasn't eligible for the game.
Just a week ago, Chelsea was also eliminated from the League Cup by Arsenal in the semi-finals and Conte's second season in charge is proving much tougher than his first.