WATCH: Fifty up for Auba as Arsenal boosts top four hopes

Introduced in the 78th minute for Jarrod Bowen, who had earlier set up goals for Tomas Soucek and Michail Antonio, Yarmolenko coolly slotted home at the end of a swift counter-attack to stun Chelsea.

The vital result lifts David Moyes' side three points above the relegation zone, while Chelsea - for whom Willian scored twice, including a stunning free-kick - missed the chance to climb to third.

It is the first time the Hammers, which won the reverse fixture 1-0, have done the league double over the Blues since the 2002-2003 season, although they were somewhat ominously relegated in that campaign.