He didn't "take the round off".
He was tired.
Moreover, it doesn't matter how it looks or how the rounds are spread out.
In a fight full of 10-9 rounds, if you take three of them you win. It could be the first 3, last 3, spread out, with him looking like crap in the title rounds, or anything else.
Maybe he specifically dumped an abnormal amount of cardio and energy into those three rounds with that specific plan in mind (win the first 3 and stay alive the last two...I wouldn't agree with that strategy but it is a possibility)?