Jamie Redknapp told Sky Sports that the 'monstrous' Mohamed Diame was the catalyst as West Ham came from behind to defeat 3-1 Chelsea at Upton Park.
The Hammers went a goal down on Saturday lunchtime courtesy of a Juan Mata strike (13), but rallied after Diame's half-time introduction, with the Senegalese midfielder's 86th- minute finish being sandwiched by Carlton Cole's equaliser (63) and Modibo Maiga's effort (90).
Sam Allardyce's side's triumph was a timely tonic after a run of just one win in six and successive defeats to Tottenham and Man United - and Redknappp says the Irons richly deserved the three points.
"West Ham were so passive in the first half and didn't lay a glove on Chelsea and Juan Mata was ghosting into positions and playing at his own pace," said the former Liverpool star.
"But as soon as the big monster (Diame) came on, it all changed. He was top class; he was aggressive, he won every single tackle, he got after Ramires and Mata - and the complexion of the game changed.
"West Ham then started to get crosses into the box and pushed up the pitch 10-15 yards to engage on Chelsea's midfield and we didn't see Mata in the second half, bar his free kick that hit the post. Diame was Yaya Toure-esque and Chelsea couldn't handle his power.
"I could see Allardyce's thinking in playing two holding midfielders (Mark Noble and James Tomkins) but they weren't getting on the ball enough, so he deserves credit for making the change at half time as it really worked."
Chelsea's defeat means they have picked up just two points - and scored just one goal - in Rafa Benitez's three games in charge, and Redknapp believes the Stamford Bridge brood are suffering without their English talisman.
"Benitez will be worried that Chelsea's midfield was dominated in the second half against West Ham and they do miss a big player like Frank Lampard," added the ex-engine roomer.
"He can stand up and man up when then other team is in the ascendancy and Chelsea didn't do that at Upton Park; a few players went missing.
"Eden Hazard, Mata and Oscar are wonderful technicians but at this stage of the season, when it is game after game, you need your big hitters."
Redknapp's fellow Sky Sports pundit Alan Smith added: "It was a game where they would have wanted John Terry at the back to bang a few heads together as balls were coming into the box, Chelsea were under the cosh and were having an awful time of it."
Under-fire Blues striker Fernando Torres fired a blank for the eighth Premier League match in a row, and while Smith reckons the Spaniard, so lethal during his halcyon days at Liverpool, can get back on the scoring trail, he thinks Chelsea do need another frontman.
"It is terrible mismanagement that a club of Chelsea's stature should be left with one centre-forward to depend on," said the former Arsenal hitman.
"Whether he has pace or not he will get chances, but his confidence is on the floor - and if you've got a centre-forward in form and converting chances, it is going to make a massive difference to the team."