Chelsea travelled to the London Stadium dreaming of a win to maintain their lead at the top of the table, with the likes of Manchester City and Liverpool closing up on them.
Despite improving their performance on Saturday afternoon the Blues were unable to get the needed win as they looked uncharacteristically weak in defence.
The Hammers secured an impressive 3-2 victory at home to end Chelsea’s run of 7 consecutive away London derby wins.
Thomas Tuchel named a much changed side with Thiago Silva, Hakim Ziyech, Jorginho and Reece James starting the game at the London Staduim.
The inclusion of James was certainly justified as he proved to be the brightest off both set of players on the field.
The England international created about 4 chances in the early stages of the game and helped Chelsea to pin the hosts inside their own half.
Despite their dominance, it was West Ham who could have gone ahead after a poor pass from Thiago Silva released Jared Bowen. But the striker’s effort was well off target and did not trouble Mendy in post.
Silva will make amends later as he got on the end of a Mason mount cross to make it 1-0 for Chelsea.
The Brazilian was largely unmarked, leaving him all the time to smartly head the ball past Fabianski.
West Ham responded immediately after the goal but Mendy reacted quickly to deny Soufal’s shot in the 29th minute.
Chelsea continued to dominate the game but could not add to their lead, allowing West Ham to grow in confidence.
The Hammers increased the pressure off the ball and were in position when Jorginho gave a feeble back pass to his goalkeeper.
Mendy was unable to react quickly and clear his lines, instead catching Bowen to gift the Hammers a penalty.
Lanzini who netted a stunning goal in his cameo against Manchester City netted the resulting spot kick to make it 1-1.
Mason Mount then registered his second goal in two games after scoring a beautiful volley from a pin point Hakim Ziyech delivery.
The first half ended with Chelsea recording over 60% of possession.
The Blues were forced to make a change before the stat of the second half as Kai Havertz was withdrawn for Romelu Lukaku.
The latter however was unable to make any impact as West Ham completed a come back.
With the Blues seeking a greater lead, Rudiger went on one of his runs early on but gave Ziyech too much to do with the pass and almost immediately after, West Ham equalised for a second time.
Thiago Silva cleared a ball but could not get distance on his header. Coufal played a pass inside and Bowen beat Mendy with a firm, low shot.
Callum Hudson-Odoi was given half-an-hour to bring his good recent form to the game as a replacement for Ziyech, initially in attack but soon as left wing-back after Christian Pulisic came on for Marcos Alonso.
Mount had a shot that could not beat Fabianski but West Ham had a clearer opening when an Antonio cross reached an unmarked Bowen at the far post but on the stretch, he sent it wide.
Inside the final quarter-of-an-hour, a Jorginho shot was deflected wide and another Thiago Silva header from another Mount corner caused momentary pandemonium, but there was a big blow to come.
There were 87 minutes played when Arthur Masuaku collected a throw out wide and decided to have a lash towards goal. Loftus-Cheek was closing the shot down but the ball took a big deflection off him, ensuring Mendy could not get across to keep the ball out.
It was always likely this would be a difficult fixture against in-form and committed local rivals, and so it proved.