The Baggies were in cruise control after Romelu Lukaku had put them 2-0 up but Reading scored three goals in the last nine minutes to snatch victory from the jaws of defeat.
"It was a struggle today. We had to stay in the game and they didn't get the third goal, which would have finished the game off," McDermott said.
"If you get a goal back, anything can happen.
"We have been 4-0 up and lost 7-5 this season. We have been on the wrong end of some high scorelines. Today we are on the right end and I am happy.
"The real Reading is the last eight minutes because e that is what I have seen over the last three years - a phenomenal character, desire and resilience.
"You don't normally win games when you are 2-0 down. We have a dressing room that is all going in the same direction. It is a big win for us.
"Pavel's shots-to-goals ratio is phenomenal. He didn't stop running. He is an absolute team man, as they all are, and it was a terrific finish for the third goal."