I think it was .. It came out of nowhere. Now look at another great legendary knockout Hearns vs. Duran, and that was not a legit one punch. Hearns had knocked him down and punched him around for two rounds. The last punch was just the end of all the punches.. But Manny was not rocked prior to that punch. it was shocking to be honest. I do wonder if his foot hitting Marquez made him distracted.
I thought it was. But apparently, since Marquez lands punches on Manny in the rounds prior to the KO, you cannot call it a one punch KO. The only one punch KO in history is when John L Sullivan ended a fight in 29 seconds with one blow.
He feinted a few times, the wind off his shoulder movement would have had a big effect on his opponent, not a 1 punch knockout I'm afraid.