We must win the midfield battle, that means keeping Sandro shackled down.
If we actually have enough players, I'd consider playing 3 in midfield. Sanchez has been poor but I think QPR is one side who he might do well against as they lack pace and can't pass it round us. This won't be a game of shadow chasing on our part.
I'd sit Sanchez and not having him doing to much chasing, just guarding in front of the CH's. If he chases the ball carrier too much he's normally a day late getting there, so he can let them try and get round him instead. I'd also have him helping the CH's deal with Zamora's aerial threat.