Pirlo is absolutely terrible on the pitch defensively. Again, he was besides James, and let him run freely into the box, leaving Chiellini stranded on his own... Chiellini was clumsy and poor defensively, but that situation happened because Pirlo couldn't be bothered to stay with James.
Pereyra should have started. Marchisio would have never let that happen.
And Barza > Chiellini. Much more solid 1v1 like that.