West Ham started the game with one centre half and finished it with none. Ultimately, it proved decisive.
For 86 minutes, Craig Dawson repelled everything Chelsea could summon to throw at goal.
In truth, this did not amount to much in the first half, but the home side gathered momentum and created more after the break, only to be frustrated time and again by Dawson making blocks and courageous tackles, winning headers and organising his team like a last-action hero.
Christian Pulisic came off the bench to rescue Chelsea with a 90th minute winner against West Ham at Stamford Bridge
The American forward immediately ran over to the stands to celebrate his last-gasp winner with the Blues fans
Pulisic was also seen celebrating his goal with his Chelsea team-mates, Romelu Lukaku (middle) and Jorginho (right)
Until one lapse in concentration as he tired. Romelu Lukaku, freshly on as a late substitute, rolled him on the edge of the box as they contested a ball headed forward by Thiago Silva, felt a hand on his shoulder and hit the deck.
It was a penalty and, after the intervention of VAR, a red card for Dawson. There was little post-match sympathy from David Moyes, who thought his defender could have nipped ahead of Lukaku to win the ball before he turned.
‘I thought he could’ve got there with his left foot and toe-poked it away,’ said his boss.
Lukasz Fabianski had little trouble saving Jorginho’s feeble effort from the spot, but this was not the end of the matter.
Chelsea continued to pour forward and when Marcos Alonso whipped in another low cross from the left, in the 90th minute, there was another sub, Christian Pulisic, to sweep the ball into the net from roughly the place where Dawson was no longer on guard.
Pulisic’s goal came just moments after Jorginho had his their penalty saved by West Ham goalkeeper Lukasz Fabianski
Jorginho rolled the ball straight down the middle of the goal – making it an easy save for the stopper (pictured above)
The thrill of late victory brought relief for Blues manager Thomas Tuchel as his team ended an unlikely sequence of three home defeats to consolidate their place in third.
West Ham retraced their steps across the capital with nothing, although the Premier League appears to no longer be their priority. Moyes opted to start several key players on the bench, with Thursday’s Europa League semi-final against Eintracht Frankfurt in mind.
Declan Rice came on for half an hour, Jarrod Bowen for 20 minutes and Michail Antonio did not come on at all. Nor did he look as if he expected to. At one point he jogged down the touchline for a stretch in a baseball cap.
Tuchel’s plans were hit in the warm-up when Andreas Christensen withdrew suffering stomach cramps. He had been forced off at half-time during the defeat by Arsenal on Wednesday.
Trevoh Chalobah was drafted into a back-three with Ruben Loftus-Cheek deputising at wing-back because Reece James was also absent, feeling discomfort in a hamstring. And there was no Antonio Rudiger, still out with a groin injury after informing Chelsea of his intention to leave at the end of the season.
Chelsea were awarded the spot-kick after Craig Dawson (right) pulled striker Lukaku (middle) down inside the box
Referee Michael Oliver went over to check the pitch-side monitor before awarding a red card to West Ham’s captain, Dawson
Both teams trundled through the first half at pedestrian pace with very little fluency or imagination and not a shot on target at either end. West Ham’s Andriy Yarmolenko came closest, firing narrowly wide.
Chelsea failed to stretch West Ham’s makeshift back-three, featuring full backs Ben Johnson and Aaron Cresswell either side of Dawson with centre halves Angelo Ogbonna, Kurt Zouma and Issa Diop all out injured.
‘It’s very hard to play spectacular open football against West Ham,’ said Tuchel but, thankfully, the second half produced more urgency and incident.
Chelsea made the running but Dawson blocked one effort from Timo Werner and deflected another by N’Golo Kante, sending it swerving towards goal. Fabianksi was able to adjust and make the save.
It was his first of the game, almost an hour into the contest. He made another, this time from Chalobah who ventured forward and took aim from distance.
Oliver sent Dawson off because he was guilty of denying a goal-scoring opportunity when he pulled Lukaku down
Moyes was first to make a change, sending on Rice to replace Mark Noble with little more than an hour gone. West Ham quickly fashioned their best opening as Pablo Fornals released Yarmolenko on the right, but Edouard Mendy narrowed the angle and smothered his shot.
As the game loosened up, Chelsea became more of a threat. Dawson made another vital block to deny Mason Mount and Werner slammed the rebound into the side-netting. Alonso headed over and Fabianski saved from Werner.
Tuchel’s team were already well on top when he made a triple change. On came Hakim Ziyech, Lukaku and Pulisic and they helped Chelsea over the line.
Lukaku, for whom very little has gone to plan recently, won the penalty and drew the dismissal of West Ham’s best defender. Pulisic then fired the winning goal.
Re-live the action from Stamford Bridge with the updates from Sportsmail’s CHARLOTTE DALY below…