On the only other occasion when West Ham United scored first against José Mourinho’s Chelsea, way back in April 2006, they ended up losing 4-1 against 10 men. When Mauro Zárate rammed in West Ham’s opening goal on Saturday the mind drifted back to that awesome show of force and character at Stamford Bridge nine years ago, an afternoon when Michael Essien ruled midfield on his own, Didier Drogba became a human wrecking ball up front and Chelsea demonstrated how adversity brought the best out of them.

They were like that during Mourinho’s first spell: tough, resilient, a team packed with strong characters whose competitive instincts so often overwhelmed their opponents, and beating West Ham that day effectively confirmed Chelsea’s second consecutive title. Yet the old togetherness is only visible in short bursts these days and the second Mourinho era is in danger of ending in bitter acrimony after Chelsea lurched deeper into crisis with a performance that reeked of indiscipline on and off the pitch at Upton Park.

Mourinho, who watched the second half from the directors’ box after speaking to the referee, Jon Moss, during the interval, is hanging on to his job. Even though Chelsea lie in 15th place after losing for the fifth time in 10 league matches, this was their first defeat since the manager was given a vote of confidence by the club’s board after they lost 3-1 to Southampton on 3 October. However, Roman Abramovich is unlikely to be impressed by an increasingly toxic situation and the sense is growing that too many of Chelsea’s players are not behind Mourinho, who will be under immense pressure if Jürgen Klopp’s Liverpool win at Stamford Bridge this Saturday.

The champions – yes, really – could be hit with a host of disciplinary charges after losing 2-1 to West Ham, who built on their wins against Arsenal, Liverpool and Manchester City by beating a Mourinho side for the first time in nine attempts.

Chelsea well and truly lost the plot when Nemanja Matic was sent off for a second booking in the 44th minute. Two players were then booked for taking their protests too far and Matic was swiftly followed down the tunnel by the assistant first-team coach, Silvino Louro, who was dismissed for haranguing the fourth official, while Mourinho disappeared from the dugout after the break. Chelsea will face a mandatory fine from the Football Association after they ended the match with six yellow cards. The Premier League is also likely to punish Mourinho after no one from the club turned up for the post-match press conference.

The FA will wait for Moss to complete his report before deciding whether to take further disciplinary action against the manager. Chelsea are appealing against the FA’s decision to impose a £50,000 fine and one-match suspended stadium ban on Mourinho for improper conduct following his criticism of Robert Madley, who officiated the defeat to Southampton, and it is understood that Saturday’s events will not trigger the stadium ban, which relates to comments made to the media rather than his touchline conduct. Mourinho could be let off if Moss says that he sent him to the stands in order to cool the tense atmosphere.

Confusion reigned. “We walked out and someone said he’d been sent off,” said West Ham’s James Collins. “I could see he was waiting to speak to the ref.”

Whatever decision the FA reaches Chelsea need to concentrate on playing football. There is a fine line between a siege mentality and a paranoid assumption that everyone is out to get you.

Chelsea, who visit Stoke City in the Capital One Cup on Tuesday, did not play too badly in the first half. Kurt Zouma was denied an equaliser by the finest of margins, his header cleared by Manuel Lanzini when most of the ball had crossed the line, and Cesc Fàbregas had a goal correctly disallowed for offside. A sense of injustice helped them mount a brief fightback against West Ham, with Gary Cahill equalising in the 56th minute.

Yet Chelsea retreated. They have conceded two or more goals in eight of their 10 league matches this season and Slaven Bilic’s decision to send on Andy Carroll paid off when the striker headed in West Ham’s winner.

West Ham, a surprising presence in the top four, were the better side and Carroll’s first goal since January was a moment of pure ecstasy for a player who has worked hard to return from the knee injury he suffered in February.

“It has been tough for him but he is going to benefit from the hard work he has done in the last eight weeks or so,” Bilic said. “It was boring work that he has never done so far in his career to get his muscles and his fitness back up. He does not have to be fit to score goals like that but the way he was pressing and everything else, he is fit.”

While West Ham rejoiced, Chelsea fumed. They created little in open play and Fàbregas was withdrawn at half-time after another meek performance.

Mourinho’s fall from grace has been sharp and shocking. Chelsea are a shambles at the moment. Is there a way out?

Man of the match: Cheikhou Kouyaté (West Ham United)