I don't quite understand what you're saying about PDC and Marchisio though. Marchisio started out wide on the right, which also points to having 4 midfielders at the start, meaning PDC on the left. Marchisio started drifting and the got in eachother's way. When Marchisio swapped sides to the left, they only got in eachother's way a few times in possession, but you could clearly see PDC's positioning was alot further back. I don't see the problem, it's pretty clear. Just because our left 'winger' is really a LB and tends to / has to fall back a bit, doesn't mean it's a 4 man defense.
But like I said to the other guy, let's agree to disagree, but in my eyes it was really obvious the intention was to play with 3 in defense up until one of the subs.