Chelsea are supposed to be a changed club. The days when Luiz Felipe Scolari was shown the door in February of his first season, André Villas-Boas was cut adrift in March or Roberto di Matteo, fresh from a European Cup triumph, dumped unceremoniously in late November are apparently long gone. Yet this is the kind of wretched occasion prone to leave a livid hierarchy flicking through a list of potential interims as they contemplate a return to chopping and changing. Head coaches, after all, have been condemned by defeats far less emphatic.

Maurizio Sarri had spent most of the second half here scribbling frantically in a notepad while his team were shredded, brutally and brilliantly, out on the pitch by Bournemouth. The hosts had only recently emerged from a run of 11 defeats in 14 games in all competitions but poured through Chelsea’s panicked and pathetic ranks, their counterattacks carrying all the bite and incision their opponents have lacked since the late autumn, sensing little to no resistance en route. The notes could express nothing else but horror.

Not since 1996 have the London club endured a league thrashing of this magnitude. In other words, Roman Abramovich has never had to digest a loss so unpalatable. All of which makes this situation feel far more volatile than it might otherwise have been. This is actually uncharted territory, for all Sarri’s post-match insistence that he felt more “frustrated” than under pressure. The Italian had cast his coaching staff from the away dressing room and, while they shivered outside, spent an hour with his players attempting to piece together what had gone so hideously wrong.

This, after all, was arguably a defeat far more insipid than that at Arsenal earlier in the month which had prompted Sarri, in his native tongue, to lacerate his players in public. He has already used the stick, and there is no appetite for carrot. “Maybe we are not at the top of the Premier League at the moment, but we are competitive and we cannot lose 4-0 against Bournemouth,” he mumbled once he had emerged. “I want to respect Bournemouth, and you know I like very much the coach Eddie [Howe], but it’s impossible to lose 4-0 here.”

Only César Azpilicueta and David Luiz dared to approach a disgruntled away support to offer their apologies after the final whistle though, by then, plenty had ventured out into the night and away. Those who watch this team consistently are finding everything, from tactics to substitutions to meek and feeble displays, grimly predictable at present. They had whipped up a chorus of “You don’t know what you’re doing” to greet Gonzalo Higuaín’s withdrawal when their team’s deficit was two. Sarri needs Higuaín, a player he convinced the board to buy, to make an immediate impact. The Argentinian’s Premier League debut amounted to being flagged twice for offside, and not a single shot fired off or chance created.

Not that this defeat was down to the 31-year-old loanee from Juventus. Higuaín was just the latest Chelsea forward struggling to provide some bite for a team who ping passes with little intent, whose movement off the ball can become aimless, before desperation sets in. They had needed to shift the ball far more quickly during a first half when they were actually on top, but they never went closer than Mateo Kovacic’s early header that was tipped on to the crossbar by Artur Boruc. Bournemouth’s threat, as sporadic as it was at first, always carried more menace, not least because this Chelsea team are only ever one concession from a collapse. Retreat almost exactly a year and the Cherries had won 3-0 at Stamford Bridge. This time, they would run riot on home territory.

The home side’s ruthlessness was utterly admirable, the slick nature of their passing and movement putting the Carabao Cup finalists to shame. There was Ryan Fraser’s clever flick for David Brooks, and the Welshman’s precisely weighted pull-back into space for Josh King to dispatch and force Bournemouth ahead. Then the combination play between King and Brooks around the hour mark, with Brooks cutting inside a befuddled David Luiz to slide in a second beyond the exposed Kepa Arrizabalaga.

King, with a splendid finish from Junior Stanislas’ pass, and the substitute Charlie Daniels would complete the rout. The home side did not even need their top scorer Callum Wilson, who has undergone a minor knee operation to flush out the joint, to run amok. They were as brilliant as Chelsea were dreadful. The visitors’ goal difference had taken such a pounding by the end that they had even slipped behind Arsenal in the table. The six-point advantage they held only a few weeks ago is a distant memory, and the scrutiny is all on a head coach struggling, still, to comprehend why.