Spending close to £1bn in the space of a year has not stopped Chelsea from making the same old mistakes. They were dominant for long stretches at the London Stadium, their football easy on the eye, but the defence remained frail, the missed chances piled up and a team packed with promising youngsters fell to a first defeat under Mauricio Pochettino after a ruthless and resilient West Ham once again proved that life under David Moyes is by no means dull. Against the odds, a feisty contest ended with Lucas Paquetá shielding the ball deep on the left and tormenting Chelsea with his flicks and tricks. West Ham’s No 10 enjoyed himself, quashing fears that he would not be in a mental state to play after the revelation that he is being investigated by the Football Association for potential betting breaches, and showed why he was a target for Manchester City. Moisés Caicedo could not get close to Paquetá. It ended as a debut to forget for Caicedo, who conceded the penalty from which Paquetá made it 3-1 deep into added time. Chelsea’s £115m signing had stepped off the bench with his new side in trouble, breached at the start of the second half when Michail Antonio punished Axel Disasi by restoring West Ham’s lead, but his impact was minimal. There has been so much change at Chelsea and, while there were some positives for Pochettino, all that money is yet to create a cohesive unit. Perhaps that was why Chelsea crumbled after Antonio’s goal, offering little in the final third even after West Ham were reduced to 10 men when their centre-back Nayef Aguerd picked up a second booking with 23 minutes left. West Ham had more nous and they could delight in their new midfielder James Ward‑Prowse outshining Caicedo by filling the void left by Declan Rice’s departure and marking his debut with two fine assists. “He did a great job,” Moyes said. “We played against a really good Chelsea team. To come away with a positive result was enormous.” It was not long before Ward-Prowse was showing why Moyes, who said he had no doubt about starting Paquetá, fought so hard to sign him. It almost felt unfair, a side with West Ham’s record at set pieces adding Ward‑Prowse to their armoury, and Chelsea immediately looked nervous. They survived the first corner from Ward-Prowse, Robert Sanchez denying Tomas Soucek, but not the next. Conor Gallagher did not even get off the ground as Aguerd headed past Sanchez. “I am so disappointed with the first goal,” Pochettino said. The frustration gnawed at Chelsea’s head coach. Pochettino was pleased with his side’s response to the early setback, Carney Chukwuemeka levelling with a stunning goal, but there was criticism for Mykhailo Mudryk, the £88.5m winger failing to take his chance after coming on at half-time. “I think he needs to be more desperate to score,” Pochettino said of Mudryk, who is yet to score since joining Chelsea. There was one opening for Mudryk when Chelsea were chasing a late equaliser but his volley almost went out for a throw. Pochettino, no doubt, will note that there was far more balance before the Ukrainian replaced the injured Chukwuemeka. Chelsea were superior during the first half, attacking at speed, and Enzo Fernández was soon threatening with a lovely pass through to Nicolas Jackson, who looked for a penalty after being fouled by Alphonse Areola. West Ham were relieved to see that Jackson had already been flagged offside but the striker was keeping Aguerd and Kurt Zouma worried. Chelsea pushed and Jackson, who has to be more clinical, headed over. The equaliser was coming and it arrived when a poor clearance from Zouma fell to Chukwuemeka. The 19-year-old beat Soucek and lashed in his first goal. The mood shifted and Chelsea should have been ahead when Soucek chopped Raheem Sterling down. Fernández’s technique betrayed him, though, and Areola saved the Argentinian’s penalty. West Ham sought to capitalise on Fernández’s profligacy, Paquetá hitting the woodwork, and emerged with more intensity in the second half. They threatened when Malo Gusto, deputising for the injured Reece James at right-back, lost Saïd Benrahma. Then Disasi’s slack pass allowed Ward-Prowse to release Antonio, who shoved Levi Colwill aside and smashed past Sanchez from 20 yards. Only now did Pochettino turn to Caicedo and there was another twist when Aguerd departed. Yet Moyes simply responded to going down to 10 men by stiffening his defence, Angelo Ogbonna coming on, and West Ham locked it down. Noni Madueke threatened with a deflected shot after coming on but Chelsea had few ideas and Paquetá came alive. Deep into added time the Brazilian’s backheel found Emerson Palmieri and in lunged Caicedo. It was over to Paquetá to finish Chelsea off and leave Pochettino waiting for his first win of the season.