The wild exchange at the end of the fourth round began with Ortiz battering Mayweather against the ropes, and then landing a head-butt to Mayweather's chin. The referee, Joe Cortez, immediately stepped in and admonished Ortiz for the head butt, taking the point away.
With that, Ortiz went over to Mayweather, kissed him on the cheek and apologized. Cortez wasn't even looking at the two of them at that point, and Ortiz seemed to think the fourth round had ended. But the round wasn't over, and Mayweather drilled Ortiz with a huge 1-2 punch, knocking Ortiz flat on his back. Ortiz wasn't able to get up as Cortez counted to 10, and Mayweather won by knockout.
After the fight, the crowd at the MGM Grand in Las Vegas booed Mayweather, who blamed Ortiz for the head butt and said he himself had done nothing wrong.
Mayweather vs. Ortiz Results | Mayweather's KO Unsportsmanlike?
"I got hit with a dirty shot," Mayweather said. "It's protect yourself at all time. I hit him with a left hook, right hand, and that ended the bout."
As he looked at a replay of his knockout, Mayweather said he had no remorse for hitting Ortiz when Ortiz didn't know it was coming.
"We're not here to cry and complain what he did dirty or what I did dirty," Mayweather said. "I was victorious. If he wants a rematch he can get a rematch."
For his part, Ortiz said he thought Cortez had called timeout in the fight at the time Mayweather knocked him out.
"It was called a break by the referee," Ortiz said. "I obeyed. I obeyed, exactly as I was told. I looked at the ref, I looked up, and then -- boom! -- I was out."
Ortiz apologized for the head butt and said he wasn't attempting to butt heads with Mayweather intentionally. And he wasn't blaming anyone, either Mayweather or Cortez, for his knockout loss.
"I'm not perfect," he said. "No one is, and neither is the ref."
In boxing, very little is perfect. And this fight had the most imperfect of endings.