West Ham started the game with one centre-half and finished it with none and, ultimately, it proved decisive.
For 86 minutes, Craig Dawson repelled virtually everything Chelsea could summon to throw at goal.
In truth, this didn't amount to very 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 those around him like a last-action hero.
Until one lapse in concentration as he tired.