Brian McDermott was left 'gutted' after Fernando Torres' offside goal helped Chelsea beat Reading 4-2 on Wednesday.
The Royals were on course for a 2-2 draw at Stamford Bridge when the officials allowed Torres' goal to stand with nine minutes remaining.
Chelsea went on to win and a 'gutted' McDermott confirmed he confronted the assistant referee he accused of costing his side a famous result against the European champions.
McDermott said: "He (Torres) was offside and it was not a good night for him (the assistant).
"It's not been a good night for me, either."
He added: "I just said to him he'd got it wrong.
"My gut feeling was that it was offside, and it was clearly offside. Unfortunate for him.
"He said he'd have a look at it. He can have a look at it. That's life.
"People makes mistakes, and he's made a mistake tonight.
"It's just a shame it was for such a crucial goal because we would definitely have got a point.
"I'm really disappointed for the players.
"We didn't deserve to lose the game. I thought we were going to win it when we got to 70-odd minutes."
Reading held a shock 2-1 lead until the 69th minute when their keeper Adam Federici gifted Gary Cahill an equaliser.
It was Federici's second howler in five days after gifting Stoke a goal in their 1-1 draw on Saturday but McDermott backed his keeper to bounce back.
He said: "I'm not concerned about him at all. He's got fantastic mentality.
"It's like everything: once a result has happened, you have to box it off. You can't affect that. You have to move on.
"He's not overwhelmed by the Premier League. It was just one of those things.
"The shot's moved and it's gone in. That's life. Nothing we can do about that now."