Chelsea legend Tommy Langley thinks a handball not being given against Ander Herrera in the early stages at Old Trafford was a big factor in the Blues losing 2-0.
Manchester United took the lead with just seven minutes on the clock after Herrera played in Marcus Rashford, who made no mistake in firing past Asmir Begovic.
However, there was controversy as the Spaniard appeared to handle the ball to bring it under control and Langley thinks the foul not being given meant Chelsea were up against it straight away.
The Blues legend says the goal gave Manchester United all the momentum and was the catalyst for the Red Devils to go on and win the game.
"These games hinge on crucial decisions which create momentum", Langley said on Chelsea TV.
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"For me, seven minutes in he makes a decision which give them the lead and momentum, and puts us behind the eight ball.
"No matter what anyone says about the 90 minutes in general, that was the catalyst for us being behind the eight ball.
"Yes, we didn't react well to it and we were poor", he added.
Langley also bemoaned the referee getting the decision wrong when he was so close to Herrera.
"How does he get it wrong when he's stood three or four yards away?"
Chelsea will now bid to quickly shrug off the defeat as they prepare to meet Tottenham Hotspur in the FA Cup semi-finals next weekend.
The Blues have lost two of their last four games and will not want the rot to set in, especially not against the side currently trying to reel them in at the top of the Premier League standings.
