McDermott's Barclays Premier League new boys were on course for at least a 2-2 draw in their opening away game at Stamford Bridge when the officials allowed an offside-looking Fernando Torres goal to stand.
Admitting he had made a beeline for the assistant who kept his flag down after the final whistle, a "gutted" 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. 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."
Indeed, npower Championship winners Reading held a shock 2-1 lead until the 69th minute, having bounced back from Frank Lampard's penalty through Pavel Pogrebnyak and Danny Guthrie's first goals for the club. The latter came courtesy of a Petr Cech howler but it was not only the Chelsea goalkeeper and officials who messed up.
Reading keeper Adam Federici had a nightmare of his own for the second time in five days to gift Gary Cahill an equaliser.
Chelsea boss Roberto Di Matteo said he had yet to see Torres' goal, which also allowed Branislav Ivanovic to kill off Reading on the break.
"I looked at the linesman straight away and he gave it straight away, so I can't comment," said Di Matteo, who was pleased to see his side go top of the Premier League for the first time since November 2010.
He said: "We are very pleased with six points after two games. I was very happy with the team performance for long periods of the game. We lost a bit our composure after Reading scored the equaliser and second goal, but we'd started off very well, with some great football, and finished off very strongly."