You can't judge Barao's performance based on what happened after he got knocked down. The question is why he got knocked down in the first place. And the strange thing is, it wasn't a very clever, intricate set-up. TJ feinted low with his lead hand, then delivered a straight cross to the chin. There was no crazy footwork, no Ali shuffle.
The punch that pretty much decided the fight (taking nothing away from TJ's performance throughout the fight) was nothing spectacular. So you have to wonder why it landed on Barao.
If Barao was dealing with some kind of injury or illness, we would have known about it. He's a Brazilian, for God's sake.