There was one point in the first half where he let Joelinton get across the front of him for a free header at goal. If he had more to do and against better players, his poor awareness and lack of aggression would be a problem. This game suited him perfectly and he was very good.
Even with his faults, he's comfortably better than Mustafi and deserves his spot. I'm not sure it'll be long before David Luiz is in ahead of him though.