The title-chasing Blues were on course for the points at the Madejski Stadium prior to Le Fondre's intervention.
The former Rotherham striker converted Hope Akpan's through ball in the 87th minute before levelling the match deep into injury time with the last kick of the game.
McDermott acknowledged his side were up against it at 2-0 down and felt the introductions of former Crawley man Akpan and Le Fondre gave the home side some much-needed impetus.
"We're trying to stay in the game. We were trying to find a solution from somewhere. The guys off the bench made a difference," McDermott told Sky Sports.
"There wasn't much in the game. They got the second. With 10 minutes to go it didn't look good.
"When you've got Le Fondre anything can happen. He is a bit special. Those two finishes were from the top drawer.
"They are the champions of Europe. These are world-class players. If you're 2-0 down to them with ten minutes to go you feel you've got real problems.
"Once you get a goal things can change and that's what happened tonight. I was so proud of our players tonight.
"We have players with massive hearts. They give us everything. We're doing everything we can be to be in this league next season."