Nah even before Sissoko came on he let Son skip past him a few times, Rojo was doing two jobs and Darmian was screwing up every attack he was involved in.
When a full-back is out of position, it is natural for the CB to cover up. Happens regularly for all full-backs who go upfield. That was more of the case with Son, Spurs stretching our defence. I was happy with what I saw before the Sissoko nightmare happened.