Ali's career was marked by an impressive 31-fight undefeated streak that ended with a loss to Joe Frazier. Ali later got his revenge in a rematch. But it was Ken Norton who dealt Ali his next significant defeat in 1973, winning by split decision in a major upset.
The first Ali-Norton bout was a turning point. Norton broke Ali's jaw, an injury Ali later described to Johnny Carson:
"It was a hard thing … At that point I didn't know if it was broken or not, but my whole system was off and it was a bad, bad feeling – to move your mouth and something's just broke. Throwing a punch I could feel the jaw. I had to go ten rounds without getting hit on that jaw again. I'm lucky and thankful I didn't get hurt seriously … If I'd got hit with a hard punch from a 215 pounder right on the end that was broke, [the doctor] said it could mean death."
Six months later, Ali won a close rematch by split decision. The rivals met for a third and final time three years after that at Yankee Stadium in New York City. While Ali got the nod on the scorecards, many felt Norton deserved to win.
In an uncharacteristic admission, Ali said after the fight:
"Kenny's style is too difficult for me. I can't beat him, and I sure don't want to fight him again. I honestly thought he beat me in Yankee Stadium, but the judges gave it to me, and I'm grateful to them."
Norton's reaction to the decision was raw:
"If you saw the look on Ali's face at the end, he knew I beat him. He didn't hit me hard the whole fight. Then they announced the judges' decision and I was bitter, very bitter. Not towards Ali… he'd done his job, he was just there to fight. But I was hurt, I was mad, I was angry. I was upset… and it still upsets me."
Norton retired in 1981 with a record of 43 wins in 50 fights. He became world heavyweight champion in 1977 by defeating Jimmy Young, but lost the title to Larry Holmes by decision.
Ali's career spanned many more years and opponents, but Norton's style proved to be the one puzzle he couldn't quite solve.