it is nice to read that some people here have a few thoughts about the tactics and possible solutions.
i would like to compare the 4-2-3-1 with the 4-4-2 of last season.
lets not watch the defense, because its the same. just the transition from defending to attacking. last year the two defensive midfielders had only two options to play to and that were the left and the right wing (nedved and camo/marchionni) and it worked (the transition into attack). when we were playing deep we had in fact a 4-2-3-1 because del piero would fall deep to receive passes in midfield (so taking diegos position in the 4-2-3-1 but a bit further to the striker). i think the difference is not that big, but the 3 attacking midfielders especially the ones on the outside do interpret their role to static.
if we look at who is going to be marked be who in this scenario it will probably be, that the opponents right fullback is marking gio, the defensive midfielder is marking diego and the leftback is marking camo so they have all our attacking players marked PLUS amauri still plays against TWO centrebacks... not a good situation in regards of having a defensive midfielder search for a pass receiver.
so i gave you the problem, now you solve it
remember, it is often enough for an opponent to mark someone by running close to him, to prevent him from being passed to, regardless of the marker actually being able to take the ball of the pass receiver when he gets it.
so melo and sissoko have the ball and no one is UNMARKED.
i am no dr. of tactics but i have a suggestion. if the players (just talking about the attacking 3 midfielders) do shift their position to the right or the left (while we attack) the marker will just track our players and stay with him. diego would go to the half right position the the defensive midfielder would just go with him.
but what if camo and gio completely switched sides (not 1 to 1 just gio right and camo left). i mean the ball is at caceres feet and gio just moves to the right (even right of diego) to give another short pass option other then camo.
there are two scenarios that can arise from that.
A) the right fullback of them completely tracks gios run and goes over to our right side thus leaving a huge gap/space for grosso. ideal position to play a side-changing cross where grosso will have enough space to control the ball even if it is not perfectly played.
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B) the right fullback of em thinks he has to mark the space/room and not the man leaving giovinco on our right hand side without an opponent and being an easy pass receiver.
this is not the masterplan, but a reasonable way to mess up with static or space marking and will only work if the change of position is fast enough, so that their midfielders do not immediately have the chance to take over the man (mark gio when he runs over)