Graham Potter knows nothing but disappointment at Stamford Bridge. Back at the club who sacked him after less than seven painful months in charge, Potter endured the frustration of Chelsea denying his new team with two scrappy goals in an angry second half. West Ham, who played well and nudged themselves in front when Jarrod Bowen punished an error from Levi Colwill, merely had the meagre consolation of knowing that they had given wealthier rivals a scare.

This was not convincing from Chelsea, even if they rose into the top four thanks to an equaliser from the excellent Pedro Neto and a Cole Palmer-inspired own goal from Aaron Wan-Bissaka. Enzo Maresca’s side were pallid for long spells and irritation was rising before an injury-hit West Ham ran out of steam. It was not ideal to be kicking off three hours before the closure of the transfer window. A curious day at Chelsea had rolled on with João Félix flying to Milan, a loan in the offing for the underused Portugal forward, and a deal being agreed for Axel Disasi to spend the rest of the season at Aston Villa. West Ham, meanwhile, were left counting the cost of two years of botched recruitment by their recently departed technical director, Tim Steidten.

The visitors had a threadbare feel with Lucas Paquetá and Edson Álvarez joining the injured contingent and Evan Ferguson not registered yet after joining on loan from Brighton. There were two full-backs in the back three, two goalkeepers on the bench and a first start in midfield for Andy Irving, a 24-year-old Scot signed without any fanfare from SK Austria Klagenfurt last year. In the event, though, West Ham gave a good account of themselves during a slow-burn opening. There were some pretty triangles at times, a sign of Potter’s ideas taking hold, and it was not easy for Chelsea to find space. It spoke volumes that their best opening came from a counterattack which ended with Noni Madueke shooting narrowly wide from the right.

Chelsea strained to raise the tempo, with Cole Palmer heavily marked. Marc Cucurella missed with a free header, Enzo Fernández dragged a shot just wide after a mistake by Mohammed Kudus, Jadon Sancho curled over and there was concern when Nicolas Jackson went down clutching his hamstring. Marc Guiu looked ready to come on, only for Jackson to insist that he was fine to continue. The game trundled on. West Ham had their moments. Kudus had a chance, Irving volleyed over from 20 yards and Bowen, leading the line with power and commitment, had two bites at turning in a corner. Filip Jörgensen did well to deny the West Ham captain with his feet.

Jörgensen had been given a huge cheer by fans delighted to see him replace Robert Sánchez. The Swede, though, was not entirely convincing. He spilled an early cross from Irving and one kick went straight to Emerson Palmieri. Chelsea, sleepy and vague, were asking for trouble. It was not a surprise when punishment arrived just before half-time, disaster flaring when Kudus forced Colwill into a wayward backpass. It went away from Moisés Caicedo and ran through to Bowen, who raced clear to caress a lovely shot beyond Jörgensen.

Chelsea deserved to be behind. They almost levelled through Palmer, whose free-kick drew a stunning save from Alphonse Areola, but they needed more intensity in the second half. West Ham, who were putting themselves about, had more to offer than a relentless supply of ironic chants about Irving from the away end. Sign up to Football Daily. Kick off your evenings with the Guardian's take on the world of football.

after newsletter promotion. Maresca did not wait long before putting Pedro Neto on for the ineffective Sancho and introducing Marc Guiu for Jackson, who has gone eight games without a goal. Yet West Ham were increasingly stubborn. Chelsea were short of ideas. Tosin Adarabioyo accepted an invitation to shoot and belted an effort well over. One attack featured Madueke accidentally knocking over the referee, Stuart Attwell.

Potter continued to applaud every piece of measured defending. He was restrained on the touchline. There were no histrionics. It was left to Bruno Saltor, Chelsea’s interim coach for the game after Potter’s sacking, to remonstrate with the officials about Colwill tripping Bowen in the buildup to the equaliser. It was a messy goal, West Ham unable to clear when Neto crossed from the right. The ball was turned back by Cucurella, Fernández’s shot was blocked and Neto arrived to fire in the rebound. West Ham, hoping in vain a VAR check would rule an offside Guiu had headed the ball on to Cucurella, geared up for a siege.