West Ham registered their first win at Stamford Bridge after Aaron Creswell scored the sole goal of the game in the second half.
Aaron Cresswell fired West Ham to its first English Premier League win at Chelsea in 17 years to hand a big boost to under-fire manager Manuel Pellegrini on Saturday.
Cresswell scored his third league goal of the campaign as the 1-0 victory ended West Ham's streak of eight matches without a win in all competitions.
The left back turned Reece James inside out at Stamford Bridge before curling the ball past goalkeeper Kepa Arrizabalaga in the 48th minute to condemn Frank Lampard to defeat in his first match as Chelsea boss against old club West Ham.
The Hammers sealed their first win since the 2-0 home victory over Manchester United on Sept. 22, as Chelsea struggled without injured England striker Tammy Abraham.
Pellegrini turned to 33-year-old former Millwall goalkeeper David Martin for his Premier League debut after Roberto leaked nine goals in three matches.
Chelsea paid the price for a string of wasted first-half chances, with Lampard's men surrendering an unbeaten home run of 13 league matches dating to 2002 against West Ham. Christian Pulisic headed over at the far post after Jorginho's cute ball teed up Pedro for the cross.
The visitors thought they doubled their lead when Michail Antonio bundled home at the far post after Robert Snodgrass’ cross. But a VAR check chalked off the goal, leaving Chelsea 20 minutes to turn the tide.
