In the words of head coach Sam Allardyce, the Baggies 'demolished' Thomas Tuchel's side – to end their unbeaten run under the German boss.
Here we rate the players following their fantastic display in the capital.
Exceptional at stopping goals this season, Johnstone has now taken to creating them with the England international grabbing an assist for Matheus Pereira. He did flap at one cross which led to Semi Ajayi making a goal-line clearance. But otherwise, he was solid. 7
The full-back did switch off for Chelsea’s second. That moment aside, he was exceptional and delivered a wonderful cross for Callum Robinson’s spectacular volley. 8
O’Shea looked solid before coming off with an injury in the 24th minute. He was replaced by Branislav Ivanovic, who also picked up a knock. That led to the introduction of Callum Robinson, who changed the game. 7
Rock-solid over the past few months and that continued here with Bartley putting in another towering display. 8
Back in the side, Ajayi put in a classy display with his reading of the game exceptional. He was strong, made a goal-line clearance and ended the game with a 100 per cent pass completion rate. 9
The left-back is just so dependable. Solid defensively but also bright on the ball, Townsend produced a wonderful back-heel in the build-up to Mbaye Diagane’s goal. Yet again, he was excellent. 8
There were one or two loose passes. But otherwise, Yokuslu once again proved to be an outstanding shield in front of Albion’s defence. 8
Quiet in the first half, Maitland-Niles showed his energy and battling qualities after the break to help drive Albion forward. 7
An outstanding performance from the midfielder, who put in a real shift both centrally and out wide. Excellent defensively, his positioning and reading of the game was first-class. He was also really unlucky not to score with a specular effort that hit the bar. 9
A performance too good for words? Pereira scored two outstanding goals. He registered two exquisite assists. He carried the ball well, worked relentlessly and also made some crucial interceptions. Majestic in every way. 10
Diagne’s goal will have come as a huge relief to the forward. But it was also one of the best team goals Albion have scored for years with it coming from a brilliant counter-attack. The striker also held the ball up impeccably all afternoon. 8
Branislav Ivanovic (O’Shea 24).
Callum Robinson (Ivanovic 32).
The introduction of the forward completely changed the game. Robinson’s first goal was a spectacular volley, while his second was a finish right out of the top drawer. But he was also excellent defensively with the forward constantly nipping into intercept the ball and stop Chelsea attacks. Like Pereira, he was magnificent. 9
Jake Livermore (Phillips 89).
Not used: Button, Peltier, Diangana, Snodgrass, Grant, Robson-Kanu.