The CBs should be in a zone, both facing the ball and transferring the #9's run. Instead MDL's back is turned and Bonucci can't run with him, so that's what you get.
But we had to go back to pre-historic 3 CBs and man-marking
doesn't really matter, you simply don't concede after a lost ball at 70 metres from you own goal. we were beaten by a simple, well executed counter of 2 passes, this is ridiculously careless team work.