Long scored twice, the 2nd a last minute penalty to edge Reading nearer a safe area.
McDermott said: "Shane has got really fit, he's looking after himself and we are now seeing the player we always knew we had.
"His confidence is sky high, he is winning headers and there was only one guy who was going to take that penalty.
"He deserves this form as he has been working really hard over the last few weeks.
"He has been brilliant for us but we need to start spreading the goals around the team."
McDermott was adamant that the penalty award was the correct decision but refused to get carried away after seeing his side move to within a point of safety.
He said: "We have taken nine points from the last nine and that is going to be massively important.
"That was the toughest game I've been involved in since I took over.
"The key is to live for the moment and win a game at a time."
Plymouth are falling behind leaving their manager to question the late penalty decision.
Paul Mariner said: "It is a very difficult pill to swallow.
"We didn't play well in the first half but we got back into the game and felt we had done enough to earn a point so it's very tough.
"The changes made a difference but when you are fighting at this end of the table you rely on a bit of luck and I don't feel we got that.
"It was a soft penalty and I'm not sure that we would have been given it at the other end but the referee had a good view of it and he gave it so that is that.
"But this league is not daunting. We will not throw the towel in, there is an incredible amount of football still to play.
"It's an unpredictable league, which is why it's the fourth most popular league in the world.
"Anyone can beat anyone and we will keep fighting till the end."