Chelsea remain fourth in the standings with 29 points, while Bournemouth climbed from 15th to 14th and moved four points clear of the relegation zone.
The defeat was surprising not only because it came on their home pitch, but because Chelsea largely dominated the play, with 67 per cent possession, 18 shots to 11 and five shots on goal to two.
VAR Reverses Call, Gives Bournemouth Massive Win
After Chelsea missed several opportunities to take the lead during Saturday's match, Bournemouth took advantage in the 84th minute when Dan Gosling flicked the ball over his own head and past Chelsea goalkeeper Kepa Arrizabalaga.
It was ruled offside at first, but the call was reversed after a video review, which sent Bournemouth's players into a raucous celebration:
Chelsea were rarely in danger prior to that goal, but the match as a whole was a frustrating one for the Blues since they couldn't make a breakthrough.
As Liam Twomey of The Athletic observed, Chelsea were unable to apply consistent pressure during the first half, which gave Bournemouth momentum entering the final 45 minutes:
That seemed to make the hosts press a bit during the second half, and it allowed Bournemouth to get Chelsea out of their rhythm:
Even so, Chelsea came close to scoring on a few occasions, and even one goal may have been enough to break the dam and deliver a big victory.
Bournemouth goalkeeper Aaron Ramsdale was on his game with a number of big saves, though, including this one from close range during the second half:
Chelsea's form was uneven to say the least entering Saturday's match, with two wins, two losses and one draw in their previous five outings in all competitions.
Bournemouth were playing terrible football, though, and few could have expected that they would snap their five-game losing streak at Stamford Bridge:
The victory was a much-needed one for Bournemouth since they were in danger for falling into the bottom three in the EPL table if their slide continued much longer.
Chelsea are secure in fourth for now since fifth-place Sheffield United are four points behind, but a Manchester City win over Arsenal on Sunday will make it difficult to the Blues to move up any time soon.
Chelsea will look to bounce back on Dec. 22 when they face an up-and-down Tottenham Hotspur team away from home.
Bournemouth will attempt to build on Saturday's upset win on Dec. 21 when they host Burnley in a match between two teams looking to move further clear of the relegation zone.