I usually try to avoid using basketball to convey a point but I will this time (the urge is always there for me).
I think you basically have to play a man to man / zonal composite.... or a half court/pitch press. When the opposition enter your half you then squeeze the space because your lines never get too far from each other and the space is easily recovered.
If you do that right the way across the pitch before they eneter your half you drag your formation and lines too far apart and the opposition finds space between your lines. It is also more tiring!
That said, when Sanchez closes down 2-3 of the closest team mates to him need to follow suit lest we render his efforts null and void....but he will need to do it selectively as we don't employ the same system as Barca. He can do all the tracking back he likes though!