Chelsea, fourth in the table, took the lead just before the
half-hour mark when Marcos Alonso's free kick came off the post and Christian
Pulisic scored from the rebound, the American winger's first goal under manager
Thomas Tuchel.
Two minutes later Chelsea defender Thiago Silva was sent off
after receiving a second yellow card for a reckless challenge.
West Brom used their numerical advantage to good effect as
Matheus Pereira scored two goals in quick succession in first-half stoppage
time to put the visitors ahead at the interval.
They added two goals on the counter-attack five minutes
apart in the second half, with Callum Robinson volleying home a Darnell Furlong
cross before Pereira turned provider for Mbaye Diagne.
Chelsea pulled one back to make it 4-2 when Timo Werner set
up substitute Mason Mount for a simple tap-in but West Brom scored their fifth
in stoppage time when Robinson found space and chipped onrushing keeper Edouard
Mendy.
West Brom remained second-bottom of the table, seven points
from the safety zone.