The Baggies recorded an emphatic 5-2 victory in London to keep their hopes of staying in the Premier League alive.
Chelsea had not lost a game since Thomas Tuchel took over as head coach; a run of 14 games, and had not conceded a goal at Stamford Bridge but the visitors were able to hit five past the West Londoners.
Allardyce reveals the weakest link in Chelsea’s setup was goalkeeper Edouard Mendy, and they made him the target man.
Christian Pulisic netted the opener for Chelsea but after Thiago Silva’s red card, Matheus Pereira scored twice to help the visitors go in 2-1 up at half time.
West Bromwich Albion refused to settle on their lead as a Callum Robinson brace and Mbaye Diagne’s calm finish helped seal a comfortable victory.
Allardyce has described Mendy as ‘rash’ for his part in West Brom’s first goal, which saw Pereira dink the ball over him easily.
“Letting them play out from the back for the goalkeeper would be a mistake,” Allardyce told talkSPORT when asked how he masterminded the brilliant victory.
“That may have been a tactic we used later in the game but if it works try and keep doing it for as long as possible. That’s why we played two split up front with Matheus Pereira and Mbaye Diagne.
“The press worked very, very well and there is something with their goalkeeper, who can be rash, he can rush out. If you saw the first goal we scored, he came dashing to the edge of his box and didn’t get anywhere near.
“We felt every time we went back to the goal and we put him under pressure that gave us good opportunities.
“Obviously you could say the sending off helped, playing against ten men, but you’ve got to beat what’s still a very good side.”
