Chelsea extended their lead at the top of the Premier League table by avenging their EFL Cup defeat and beating West Ham United 2-1 at the London Stadium.
It was the home side who actually started the better, dominating the early possession and putting pressure on the Chelsea defence without carving out any clear cut chances.
And Chelsea punished the home side’s failure to turn their early pressure into anything more significant, the excellent Eden Hazard rounding Darren Randolph after a swift counter to put the league leaders ahead midway through the first half.
Randolph prevented Chelsea going further ahead by saving from Pedro just before the break but shortly after the interval, Gary Cahill flicked on from the corner for Costa to prod home with his knee.
The Hammers keeper again kept his side in the game with another fine save from Costa before Manuel Lanzini grabbed a late, late consolation. Slaven Bilic’s West Ham remain in 11th spot in the standings.