Parma are obviously a poor defensive team as the stats suggested before the game, but the fluidity from Lichsteiner, the midfield 4 and Tevez is such that they have no idea who to follow. Only Llorente is a reference and still he can afford to move around and drop off. Tactically Donadoni could not plan an educated defensive set up, they basically had to get lucky and maybe grab a goal on the counter.
The system does look like we risk a bit more at the back but that's no problem as long as we are being efficient. Speaking of which, it'd be nice to see Coman get 30 mins here for Tevez, considering the Argentine is only looking for his own goal at the moment.