Chelsea became the first defending Premier League champions to concede three goals in their opening match of the season by making an abysmal start against Burnley.
Blues captain Gary Cahill was sent off after 14 minutes at Stamford Bridge and Sean Dyche's men have taken full advantage, racing into a 3-0 lead courtesy of Sam Vokes goals either side of Stephen Ward's strike.
Chelsea 14/1 to win the Champions League
That has left Chelsea reeling against a side many have predicted will find themselves in a relegation battle this season.
Unless Antonio Conte can organise his men into an astonishing comeback, they will be only the second defending champions to lose their first game of the following campaign.
Leicester City became the first last season by falling to a 2-1 loss against Hull City, but Chelsea are off to a significantly worse start.
Four defending champions have conceded two goals on opening day but only Leicester have lost, with Manchester United recording 3-2 wins in 2001 and 2012 and Chelsea drawing 2-2 with Fulham in 2015.
But the Blues, who are without the likes of Eden Hazard and Diego Costa, now find themselves three goals behind with 45 minutes still to play in west London.