if you lave your zone open, and you are too late to close down the opposing player anyway, without knowing for certain whether your look/signal was recognized and acted upon, ultimately you are at fault.
Before opening up that zone, Chiellini should have made certain that Giacherini was indeed positioned and expecting to do cover work - again, in a 3-5-2, the winger is a farther from that zone/situation than the Lb would be in a 4-4-2.