A miserable evening in Bournemouth ended with the Blues being well beaten after conceding four second-half goals, two of which were scored by Josh King, as we dropped down to fifth in the Premier League table.
Maurizio Sarri's side enjoyed the better of the opening 45 minutes and struck the woodwork early in the game as Artur Boruc tipped a diving header from Mateo Kovacic against the bar.
Despite dominating possession, however, there were few goalscoring opportunities to speak of, and with Bournemouth threatening on the break as the half progressed, Kepa made a couple of important saves.
The home side took the lead three minutes into the second half through King, who blasted into the back of the net after being teed up by David Brooks, who then made it 2-0 after capitalising on a mix-up in the Chelsea defence.
King made it 3-0 16 minutes from time, converting from a Junior Stanislas pass and substitute Charlie Daniels completed the scoring deep into added time with a header to cap a miserable night for the Blues.
Gonzalo Higuain made a second consecutive start – his first in the Premier League – while Pedro and Eden Hazard returned to form an attacking trio alongside the Argentinian striker.
Elsewhere, there was a maiden Premier League start of the season for Emerson Palmieri and David Luiz, rested at the weekend, once again partnered Toni Rudiger at the heart of the back four.
Former Chelsea defender Nathan Ake starts for the hosts, while both Asmir Begovic and Dominic Solanke were named among the Bournemouth subs.
There was a moment of concern inside the opening couple of minutes for the Blues as David Luiz went down after being struck in the side of the face by a stinging Brooks drive, but when play resumed we were quickly on the front foot and almost took an early lead.
Pedro delivered from the right-hand side and although Higuain was unable to reach it, the ball arrived at the far post where it was met by Kovacic, by no means the biggest player on the pitch, who stooped and headed towards goal, with the fingertips of Boruc diverting it against the bar before Ake cleared.
Hazard, scorer of the only goal of the game in last season’s corresponding fixture, then stung the palms of Boruc from outside the box as we looked to gain an early advantage in the contest.
The Blues were seeing plenty of the ball in the opening stages of the game and on the rare occasions we did surrender possession, both Kovacic and Jorginho were working hard to win it back with quick and high pressing.
It took until just before the 20-minute mark for the home side to register an attempt on goal and when it arrived, Andrew Surman’s long-range effort flew well over the bar.
A quick Chelsea break led to another decent opportunity as David Luiz, once again instigating from deep, picked out Hazard with a low pass. The Belgian quickly helped it into the path of Pedro who burst forward and cut inside, only to see his left-footed strike comfortably saved by Boruc.
It had been a slow start by the hosts, with the Bournemouth supporters clearly frustrated, but as the ball was worked out to Ryan Fraser on the left an opportunity presented itself. The Scot then switched it inside to Brooks, in a good position, who was only thwarted by a well-timed challenge from Emerson, with David Luiz subsequently clearing.
Bournemouth were gradually beginning to get a foot-hold in the game, as well as offering more of an attacking threat, and Kepa was called into action after Brooks was allowed to advance forward from deep, the Spaniard saving his strike low down to his left.
At the other end Boruc was called upon to push away a left-footed curler by Azpilicueta, before denying Hazard, who tried his luck from the edge of the box, soon after.
Two minutes before the break, however, Bournemouth passed up their best opportunity of the game so far. King ran at the retreating Chelsea defence and slipped the ball to his right, into the path of Stanislas, whose first-time effort was beaten away by Kepa.
Having had the better of the first half, within three minutes of the restart the Blues were behind.
A Bournemouth throw-in deep inside our half was taken quickly, and as the ball landed at the feet of Brooks, inside the box, he shifted it to King who blasted his strike into the roof of the net.
It was the worst possible start to the second half, but our response to that setback was positive and were almost back in it as Pedro picked out the run of Kante with a clever pass in behind the Bournemouth defence, the ball just getting away from the Frenchman as he attempted to bring it under control.
Willian replaced Pedro just after the hour but moments later our task was made all the more difficult when the home side extended their advantage.
A stray David Luiz pass was collected by Brooks, but as the Brazilian won it back the loose ball fell to Stanislas, who played it over the top for his team-mate to run on to. Brooks advanced towards goal before cutting back inside the retreating David Luiz and rolling his strike into the bottom corner.
Olivier Giroud came on for Higuain as Sarri attempted to freshen up the attack, but with 16 minutes left on the clock it was 3-0 to Bournemouth as King scored his second of the game.
Nathaniel Clyne slipped the ball in behind the Chelsea defence from out on the right and having set up their second goal, Stanislas was the creator once more, rolling it into the path of King who beat Kepa with a tidy finish.
Our third and final change followed soon after as Kovacic made way for Ruben Loftus-Cheek, and the substitute was quickly into the action, dragging an effort wide of the far post from Hazard's cut-back.
Our misery was compounded, though, in added time when substitute Daniels, who had only come on moments earlier, flicked a header beyond Kepa to make it 4-0.
Attention now turns towards Saturday, when we will be aiming to get back to winning ways at home to Huddersfield.
Chelsea (4-3-3): Kepa; Azpilicueta, Rudiger, David Luiz, Emerson; Kante, Jorginho, Kovacic (Loftus-Cheek 77); Pedro (Willian 61), Higuain (Giroud 64), Hazard.
Unused subs: Caballero, Christensen, Alonso, Barkley.
Bournemouth (4-4-1-1): Boruc; Clyne, Cook, Ake, Smith; Brooks (Ibe 68), Gosling, Surman (c), Fraser (Daniels 90); Stanislas (Mepham 90+4); King.
Unused subs: Begovic, Mousset, Rico, Solanke.
Scorers King 48 and 74, Brooks 63, Daniels 90+5
Referee Roger East