The fight goes like this:

Zab wins 3 out of the first 5 rounds, giving Cotto problems and stunning him at some point.

Round 5 on Cotto takes over because of all of the body shots he has landed to this point. Zab is wearing out physically and mentally. Zab then gets stopped in the late rounds.

Zab has a ton of talent but lacks the mental side of it to be able to stay fighting at the elite level. He couldnt stay focused beyound 5 rounds against PBF, and he was taking the fight to Floyd at that point. But then stopped doing what won him the first few rounds. I believe Cotto will take his will/heart/spirit away.