Reduced to 10 men and 3-0 down at the break against a team they hadn't lost to since 1971, Chelsea did rouse themselves in the second half, playing with real vigour to push Burnley back.
Antonio Conte might not be happy with the lack of discipline shown by his senior players, but the spirit and fight shown by his side should be a positive sign, although Chelsea must avoid these self-inflicted wounds in the future.
Instead, his studs caught the Belgium midfielder on the shin and while it was accidental, it was also reckless and referee Craig Pawson immediately brandished the red card.
Captain Cahill was sent off just 14 minutes into the game as Burnley went on rampage, scoring three goals in the first half.
Matt Lowton's right-wing cross found Vokes and he sent a bouncing volley into the far corner, with Thibaut Courtois unable to get across in time.
Chelsea had their first real chance at goal 11 minutes in when Cesar Azpilicueta's low cross was deflected and almost sat up for Willian to fire home in the centre of the goal. "The sending-off made a difference and I thought we did really, really well to handle that and keep the ball and create chances", he said.
With the man advantage, Burnley took the lead on 24 minutes.
With the clock winding down, David Luiz connected with a flick from Morata and pounded the ball into the goal for Chelsea's second of the game. At the hour mark, Alonso's freekick was kept out by Burnley's goalkeeper, Tom Heaton.
Chelsea, which won 17 of its 19 home games last season, became the second straight team to begin its league title defense with a loss, after Leicester last season.
While he will have been consoled by the sight of Alvaro Morata getting on the scoresheet on his debut and Luiz's thumping volley late on, Conte has been left with plenty to ponder ahead of their next match against Tottenham.
"They opened up the pitch even more with 10 men, which put us on the back foot a little in the second half, but that's to be expected".