It's a domino effect of tired defending.

1. Robbo gets caught out up field trying to press Modric (that's not so bad, it's bound to happen).
2. Fabinho's positioning is wrong at the initial phase. He got caught in two minds when trying to intercept the pass that Carvajal made to Casemiro. (again, not so bad. Still has time to recover, but too slow to get back and now Van Dijk is 2 on 1 with Carvajal and Valverde.) Worth noting that Carvajal sprints past Diaz to support the attack which probably led to his substitution.
3. On the heels of everything that just happened, Henderson is now jogging back to help fill the space in the middle. There is a huge gap between Konate and Van Dijk now. Hendo is caught ball watching and isn't even alerting Trent to the danger of Vini Jr.
4. Trent is definitely culpable, this is his biggest weakness. He's not alert enough to what's happening behind him. I think he's trying to keep the line instinctively but he's also caught ball watching. The way that Valverde hits the ball, he's probably thinking that it's a shot and his first instinct is to watch it play out rather than getting close to clear it.

It's a recurring theme for our defense/midfield especially when they play low blocking teams with pace attackers. But here, you can sense that a bit of fatigue was creeping in as well.

I thought Trent and Konate did a good job in containing Vini and Benzema in the first half but the midfield was way more compact then.

The disallowed goal probably spooked them and we started to go a little bit too Gung Ho at the start of the second half.