Real won 2-1 to reach the round of 16 with an aggregate victory of 3-1.
Courtois made a superb save on 38 minutes, which proved decisive on the night.
He later said: . "I saw a chance and I stopped it well... It goes between my legs and I'm well down, ready to stop it."
But how can such a tall goalkeeper get so far down? The Belgian explained: "It's my parents' genes, they played volleyball. And I played volleyball too.
"It's a save where you move your leg out of the way, it's called a sweep the leg, and you get well down. If I move my leg out during the movement, you get down quickly.
"It's a technique I learned at Chelsea and it comes in handy sometimes..."
Courtois made it clear that he is aware the team needs to improve.
"We lack fluidity and speed in our play with the ball; we need to move the ball more from side to side, move them around more, and if we take too long to pass, the opponent gets comfortable.
"That's what the manager asks for. I don't think we're playing great, but winning is what matters now."