The goal that got Real back into the game was 1000% on Cancelo. He completely lost the defensive line keeping Benzema on side. Then he compounded it by not staying with the mark. If you break ranks and keep someone on side on your side you better at the very least stick with the runner. Not only did he not stick with him, he then went after him casually and lazily allowing the cross in to Rodrigo. Watch him in stoppage time in the build up to Kane's goal against Tottenham.
He didn't play in the first leg against Real because he made a sloppy dangerous tackle on the edge of the box in stoppage time vs Atletico and drew a booking and a suspension. Everyone can't be great at everything. Cancelo is technically gifted, an excellent passer and dribbler, when he is on his game, which isn't always. He is a piss poor defender, especially on the left side, whenever we play someone with legit talent up top. JMO.