Thomas Tuchel suffered his first defeat as Chelsea boss following a 5-2 defeat to West Brom on Saturday evening.
Chelsea took the lead in the 27th minute and it was Christian Pulisic capitalizing on a failed rebound clearance. The Blues had a freekick from outside the box, Alonso stepped up to take it and his effort beat a diving Johnston but not the post. However, the rebound dropped at Pulisic's feet and the American side-footed home into a gaping goal.
Two minutes later, the Blues were reduced to ten men after Thiago Silva was shown the second yellow card for a tackle on Yokuslu. The Blues gave the ball in a dangerous zone and Silva rushed to tackle Yokuslu but it was a late challenge and he was given a second yellow and a red card.
In the 47th minute, West Brom drew level through Matheus Pereira. Goalkeeper Johnson had a long clearance upfield finding all the way through to Pereira who with just the advancing Mendy to beat, lobbed the keeper.
Two minutes later, just before the whistle for halftime could blow, West Brom turned the score around. Diagne fed Pereira and the Brazilian found the back of the net with a clever low finish at the near post that left Mendy helpless.
In the second half, West Brom grabbed the second through Robinson following a nice build-up.
In the 68th minute, West Brom scored another brilliant goal. Chelsea had a corner but it was cleared with Pereira and Robinson combining to release Townsend in the box. His gorgeous backheel set up the unmarked Diagne, composed himself well, and beat Mendy with a simple finish.
Mason Mount who was introduced in the second half, reduced the deficit for the Blues following a short pass from Timo Werner inside six yards.
In the stoppage time, it was five for West Brom. Pereira played Robinson in and it was a wonderful finish, lofting the ball over Mendy as the Chelsea keeper rushed out.
The last time Chelsea conceded five goals at home was almost 10 years ago - in a 5-3 defeat to Arsenal in October 2011.
As for West Brom, they last scored five goals away from home in February 2012 against Wolves.