The 'Baggies' were made to pay for Ahmed Hegazy's unnecessary wrestling match with Alvaro Morata down the left, further piling the pressure on Pulis.
From the ensuing free kick Cesc Fabregas' once again showed his sensational set-piece delivery, clipping the ball to the far post, where Alonso had been allowed to ghost in unmarked.
The full-back duly tucked the ball home, cushioning the delivery past Ben Foster and into the roof of the net.
Check out the goal for yourself below:
Marcos Alonso Goal HD - West Brom0-3Chelsea 18.11.2017 https://t.co/RmOYzGJ0KY#SofaScore #WBA #CHE
— Soccer Is Life (@FootballLive30) 18 November 2017