it did not surpass. I don't think the knockdown happened because of anything Chavez did. It was Martinez probably being older and getting tired and also taking too many chances when he had the fight won. Had he gone in and boxed he would have won the 12th easy and no one would be talking about a rematch.
I don't like all this talk of Chavez being so much bigger than Martinez. Martinez is a middleweight now. He would probably have a hard time making 154. Chavez made the weight and so did Martinez. If Chavez is too big for 160, then you could say he was drained for the fight. One thing for sure is that Martinez is not really a small middleweight. He would be bigger than Canelo.