Glenn Murray's late header gave Bournemouth a famous win at Stamford Bridge and ratcheted up the pressure on Chelsea manager Jose Mourinho.
The 82nd-minute goal, scored after Chelsea failed to clear a corner, moves Eddie Howe's side up to 17th place.
It also makes them the first promoted side to beat Chelsea at home since Charlton in April 2001.
But it leaves the defending champions in 14th place, 14 points adrift of the Champions League places.
It had appeared that Chelsea were slowly rediscovering their form after keeping three successive clean sheets in all competitions, but this defeat casts fresh doubt both on their ability to haul themselves back into the Champions League places and on the manager himself.
Mourinho's side have now lost eight of their 15 Premier League games and are just three points clear of the relegation zone at the beginning of December. The 14-point gap to the top four is beginning to look insurmountable.
Chelsea started once again without Diego Costa, only for the Spain striker - who responded angrily to being an unused substitute against Tottenham last Sunday - to be summoned at the interval.
He did offer a greater presence to a hitherto meek attack, winning the odd header and occupying the visitors' centre-backs, but could not conjure the goal that would have settled the growing nerves around Stamford Bridge.
The closest Costa came was first narrowly failing to connect with a flashing Branoslav Ivanovic cross, then having a prodded effort blocked by Artur Boruc.
It meant that his only appearance in the referee's notes was for a booking, received for tugging down Matt Ritchie.
Chelsea were unbeaten in 43 Premier League games at Stamford Bridge against promoted clubs but will rarely have faced one as confident and composed as Eddie Howe's side were.
Bournemouth were comfortable on the ball and ambitious in their use of it, which allowed them to squeeze up the pitch and cleave open their more feted hosts on several occasions.
Indeed, had it not been for returning Chelsea goalkeeper Thibaut Courtois - who had not played since the defeat by Crystal Palace in August after damaging medial knee ligaments - the visitors might have won more comfortably. The Belgian thwarted Josh King three times in the opening half after being preferred to Asmir Begovic,
However, he was unconvincing in his attempts to claim Junior Stanislas' 82nd-minute corner, his weak punch being directed back towards goal by Steve Cook before Murray planted a header into the unguarded net. Mourinho might also question Branislav Ivanovic's tame attempt to prevent Cook winning the loose ball.
More to follow.
Full Time Match ends, Chelsea 0, Bournemouth 1.
90:00 +4:27 Full timeFull Time Second Half ends, Chelsea 0, Bournemouth 1.
90:00 +3:37Foul by Willian (Chelsea).
90:00 +3:37Adam Smith (Bournemouth) wins a free kick in the defensive half.
90:00 +3:14Attempt blocked. Loïc Remy (Chelsea) header from the centre of the box is blocked. Assisted by Eden Hazard with a cross.
90:00 +1:41Attempt saved. Dan Gosling (Bournemouth) right footed shot from the right side of the six yard box is saved in the bottom right corner. Assisted by Matt Ritchie.
90:00 +1:13Foul by Eden Hazard (Chelsea).
90:00 +1:13Adam Smith (Bournemouth) wins a free kick on the right wing.
90:00 +0:27Corner, Bournemouth. Conceded by Gary Cahill.
90:00 +0:26Attempt blocked. Harry Arter (Bournemouth) right footed shot from the right side of the box is blocked.
85:53Corner, Chelsea. Conceded by Junior Stanislas.
84:46Attempt missed. Branislav Ivanovic (Chelsea) right footed shot from outside the box misses to the left. Assisted by Pedro.
83:56Attempt missed. Matt Ritchie (Bournemouth) left footed shot from outside the box is close, but misses to the left. Assisted by Glenn Murray.
83:04Willian (Chelsea) wins a free kick in the defensive half.
83:04Foul by Harry Arter (Bournemouth).
82:48 SubstitutionSubstitution Substitution, Chelsea. Loïc Remy replaces Cesc Fàbregas.
82:44 SubstitutionSubstitution Substitution, Chelsea. Bertrand Traore replaces Baba Rahman.
81:28 Goal scoredGoal! Goal! Chelsea 0, Bournemouth 1. Glenn Murray (Bournemouth) header from very close range to the centre of the goal following a corner.
81:25Attempt blocked. Steve Cook (Bournemouth) right footed shot from the centre of the box is blocked.
80:56Corner, Bournemouth. Conceded by Pedro.
Kurt Zouma (Chelsea) wins a free kick in the defensive half.
80:18Dangerous play by Glenn Murray (Bournemouth).
79:49 SubstitutionSubstitution Substitution, Bournemouth. Glenn Murray replaces Joshua King because of an injury.
78:49Attempt missed. Nemanja Matic (Chelsea) left footed shot from outside the box misses to the left. Assisted by Eden Hazard.
77:12Attempt missed. Kurt Zouma (Chelsea) with an attempt from the left side of the six yard box misses to the left. Assisted by Willian with a cross following a corner.
76:50Corner, Chelsea. Conceded by Artur Boruc.
76:48Attempt saved. Diego Costa (Chelsea) right footed shot from the left side of the box is saved in the bottom left corner. Assisted by Cesc Fàbregas with a through ball.
75:18Attempt blocked. Pedro (Chelsea) left footed shot from the centre of the box is blocked. Assisted by Willian.
74:05Pedro (Chelsea) wins a free kick in the defensive half.
74:05Foul by Harry Arter (Bournemouth).
73:46Delay over. They are ready to continue.
72:54Delay in match Junior Stanislas (Bournemouth) because of an injury.
69:55Kurt Zouma (Chelsea) wins a free kick in the defensive half.
69:55Foul by Joshua King (Bournemouth).
69:32Foul by Baba Rahman (Chelsea).
69:32Matt Ritchie (Bournemouth) wins a free kick in the defensive half.
66:55Corner, Chelsea. Conceded by Andrew Surman.
66:01Willian (Chelsea) wins a free kick on the left wing.
66:01Foul by Matt Ritchie (Bournemouth).
64:22Corner, Chelsea. Conceded by Matt Ritchie.
62:10 BookingBooking Diego Costa (Chelsea) is shown the yellow card for a bad foul.
62:04Foul by Diego Costa (Chelsea).
62:04Matt Ritchie (Bournemouth) wins a free kick in the defensive half.
59:30Foul by Diego Costa (Chelsea).
59:30Adam Smith (Bournemouth) wins a free kick in the defensive half.
56:51Corner, Chelsea. Conceded by Andrew Surman.
54:33Corner, Chelsea. Conceded by Adam Smith.
53:11Attempt missed. Nemanja Matic (Chelsea) header from very close range is too high.
52:35Corner, Chelsea. Conceded by Steve Cook.
50:53Attempt missed. Willian (Chelsea) right footed shot from outside the box misses to the left. Assisted by Eden Hazard.
48:44Attempt saved. Pedro (Chelsea) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Diego Costa.
47:10Corner, Chelsea. Conceded by Adam Smith.
46:06Attempt missed. Matt Ritchie (Bournemouth) left footed shot from outside the box is just a bit too high.
45:00Second Half begins Chelsea 0, Bournemouth 0.
45:00 SubstitutionSubstitution Substitution, Chelsea. Diego Costa replaces Oscar.
45:00 +3:01 Half timeHalf Time First Half ends, Chelsea 0, Bournemouth 0.
43:57Delay over. They are ready to continue.
43:07Delay in match Joshua King (Bournemouth) because of an injury.
42:39Attempt saved. Oscar (Chelsea) left footed shot from the left side of the box is saved in the bottom left corner. Assisted by Pedro with a through ball.
41:08Gary Cahill (Chelsea) wins a free kick in the defensive half.
41:08Foul by Joshua King (Bournemouth).
40:59Attempt blocked. Oscar (Chelsea) right footed shot from the centre of the box is blocked. Assisted by Eden Hazard.
40:09Attempt missed. Kurt Zouma (Chelsea) left footed shot from the right side of the six yard box misses to the right. Assisted by Willian with a cross following a corner.
39:50Corner, Chelsea. Conceded by Artur Boruc.
39:48Attempt saved. Pedro (Chelsea) right footed shot from the centre of the box is saved in the bottom right corner.
39:46Attempt blocked. Pedro (Chelsea) right footed shot from outside the box is blocked. Assisted by Eden Hazard.
39:09Attempt missed. Joshua King (Bournemouth) right footed shot from outside the box is high and wide to the right. Assisted by Harry Arter.
38:04Foul by Baba Rahman (Chelsea).
38:04Adam Smith (Bournemouth) wins a free kick on the right wing.
35:41Eden Hazard (Chelsea) wins a free kick on the left wing.
35:41Foul by Andrew Surman (Bournemouth).
35:07Attempt saved. Joshua King (Bournemouth) right footed shot from a difficult angle on the right is saved in the bottom right corner.
34:18Attempt saved. Eden Hazard (Chelsea) left footed shot from outside the box is saved in the bottom right corner. Assisted by Pedro.
32:41Attempt missed. Nemanja Matic (Chelsea) left footed shot from outside the box misses to the right. Assisted by Willian.
32:12Delay over. They are ready to continue.
31:21Delay in match Joshua King (Bournemouth) because of an injury.
30:57Offside, Bournemouth. Matt Ritchie tries a through ball, but Joshua King is caught offside.
28:53Corner, Bournemouth. Conceded by Nemanja Matic.
28:52Attempt blocked. Dan Gosling (Bournemouth) right footed shot from outside the box is blocked. Assisted by Junior Stanislas.
27:14Attempt missed. Pedro (Chelsea) right footed shot from the centre of the box is too high. Assisted by Branislav Ivanovic with a cross.
26:34Attempt missed. Gary Cahill (Chelsea) header from the centre of the box misses to the left. Assisted by Willian with a cross following a corner.
26:12Corner, Chelsea. Conceded by Junior Stanislas.
24:07Attempt missed. Harry Arter (Bournemouth) left footed shot from outside the box misses to the right. Assisted by Junior Stanislas.
23:23Offside, Chelsea. Cesc Fàbregas tries a through ball, but Nemanja Matic is caught offside.
22:57 BookingBooking Andrew Surman (Bournemouth) is shown the yellow card for a bad foul.
22:52Pedro (Chelsea) wins a free kick in the attacking half.
22:52Foul by Andrew Surman (Bournemouth).
22:08Offside, Chelsea. Kurt Zouma tries a through ball, but Eden Hazard is caught offside.
21:28Oscar (Chelsea) wins a free kick in the attacking half.
21:28Foul by Andrew Surman (Bournemouth).
20:40 BookingBooking Pedro (Chelsea) is shown the yellow card for a bad foul.
20:37Foul by Pedro (Chelsea).
20:37Harry Arter (Bournemouth) wins a free kick in the attacking half.
19:47Kurt Zouma (Chelsea) wins a free kick in the defensive half.
19:47Foul by Joshua King (Bournemouth).
16:47Delay over. They are ready to continue.
15:30Delay in match Gary Cahill (Chelsea) because of an injury.
14:05Corner, Bournemouth. Conceded by Thibaut Courtois.
14:04Attempt saved. Joshua King (Bournemouth) right footed shot from the right side of the box is saved in the bottom right corner. Assisted by Dan Gosling.
13:24Foul by Pedro (Chelsea).
13:24Adam Smith (Bournemouth) wins a free kick in the attacking half.
11:47Attempt blocked. Joshua King (Bournemouth) left footed shot from the centre of the box is blocked.
11:43Attempt saved. Junior Stanislas (Bournemouth) left footed shot from the left side of the box is saved in the bottom right corner. Assisted by Joshua King.
10:35Oscar (Chelsea) wins a free kick in the attacking half.
10:35Foul by Simon Francis (Bournemouth).
9:42Attempt blocked. Junior Stanislas (Bournemouth) right footed shot from the left side of the box is blocked. Assisted by Dan Gosling.
7:57Foul by Oscar (Chelsea).
7:57Junior Stanislas (Bournemouth) wins a free kick in the defensive half.
6:33Pedro (Chelsea) wins a free kick in the defensive half.
6:33Foul by Harry Arter (Bournemouth).
6:17Attempt blocked. Junior Stanislas (Bournemouth) right footed shot from the centre of the box is blocked.
5:11Corner, Chelsea. Conceded by Charlie Daniels.
4:35Oscar (Chelsea) wins a free kick in the attacking half.
4:35Foul by Harry Arter (Bournemouth).
1:38Foul by Gary Cahill (Chelsea).
1:38Joshua King (Bournemouth) wins a free kick in the defensive half.
1:25Attempt saved. Eden Hazard (Chelsea) right footed shot from the right side of the box is saved in the top left corner. Assisted by Willian.
0:00First Half begins.
0:00Lineups are announced and players are warming up.
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