Olivier Giroud sat behind the home dugout here, descending ever deeper into his new training coat as if attempting to hide from all he was witnessing. So much of this new start would have reminded him of his darker days at Arsenal. Only 24 hours previously he had been summoned from the bench in South Wales as his old team succumbed to Swansea, then the Premier League’s bottom club. Now, having been prised away by the champions, he endured having to watch his new side capitulate against another team apparently threatened by the drop.

The Frenchman was supposed to have left nights like this behind. Instead he shivered in disbelief as Chelsea succumbed to their worst home defeat since April 2016. Bournemouth were excellent, rugged when they needed to be and ruthless in a blistering spell after the break, and ended up running riot. Their first three-goal haul away to a top-six opponent must rank as their most startling top-flight victory, a game which exposes their previously lowly position as a deception.

Perform like this over what remains of the season and they will nestle more permanently in the top half, where they have now clambered. “When we won here in our first season in the Premier League it was an historic day but it was backs against the wall,” said Eddie Howe, whose team have now gone six games unbeaten in the league. “But there was no luck connected to today. It was a very strong performance throughout and a huge moment for us this season. The best performance that we’ve had at this level and a result to match.”

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Chelsea, their own eight-match unbeaten league run in tatters, suddenly look distinctly vulnerable in fourth. Their own title defence had long since faded, with this in effect a loss in a competition they stand no chance of winning. But it was the humiliation, and the looming possibility of being overhauled by Tottenham, which will have stung Antonio Conte in the dugout and, more pertinently, the hierarchy up in the directors’ box. Bournemouth have made a habit of beating reigning champions since rising to this level but the comprehensive nature of this win said much about these teams’ current trajectories. It ended up as a rout.

The visitors had frustrated Chelsea up to the break, crowding out Eden Hazard when the Belgian sought to inspire from his central brief and hinting at the threat they might carry on the counterattack. Where the hosts were lethargic, Bournemouth were energetic. Their incision would be far sharper and more obvious after the interval. Chelsea, with Conte looking on in disbelief, simply fell to pieces, unable to contain the direct running of Callum Wilson and Junior Stanislas. The home side had not conceded a goal at home in the league for 489 minutes. Yet, to gasps of astonishment from the sidelines, they would ship three in 16 minutes around the hour-mark.

Play Video 0:42 Conte insists he's doing 'great job' despite Chelsea rout – video

A defence shorn of the hamstrung Andreas Christensen merely disintegrated. Chelsea were still digesting Marcos Alonso’s near miss from a free-kick at the other end when Tiémoué Bakayoko dawdled in possession and, in the counterattack that followed, Jordon Ibe collected from the excellent Wilson and slipped a pass between Gary Cahill and Antonio Rüdiger for the striker to accept. The finish was calmly and confidently slid under the advancing Thibaut Courtois. Within minutes any hopes of recovery were choked by another incisive and precise move upfield, again featuring Wilson’s driving run and pass to Stanislas at his side. The winger finished through Courtois’ legs and Chelsea seemed broken.

Theirs was a panic the kind of which has not gripped these parts since the unravelling of José Mourinho’s second spell in charge. Another Bournemouth corner duly inflicted more pain, Chelsea failing to clear before Stanislas’ shot was flicked in by Nathan Aké, formerly of these parts, from close range. Howe described it as “the best display” he had ever overseen at Bournemouth, which says much given their rise from the third tier. The home support defiantly chanted Conte’s name, preferring to reaffirm their support of the head coach than berate the team’s disjointed display, but they can see the signs.

Too many of this squad are fatigued by their schedule, with Ross Barkley still horribly rusty and withdrawn from his first start. Others are succumbing to muscular tweaks and strains. The Champions League resumes in a few weeks and there was admirable black humour to the locals’ ironic chants of “Barcelona, we’re coming for you”. That tie looks increasingly daunting. But so, on this evidence, does Monday’s trip to Watford.