Watch | Muhammad Ali vs Joe Frazier: Fight of the century

Frazier was the unbeaten heavyweight champion, a short cannonball of a fighter with a left hook that could knock out an elephant.

New York: The money was huge — a cool US$2.5 million apiece — and so was the stage for Muhammad Ali and Joe Frazier. Their first fight at Madison Square Garden was so epic it was billed as the Fight of the Century, and 50 years later it reigns undefeated.

Frazier was the unbeaten heavyweight champion, a short cannonball of a fighter with a left hook that could knock out an elephant. Ali was, well, Ali even if Frazier insisted on calling him (Cassius) Clay as he fought his way back into condition after being banned from boxing for more than three years for refusing the Vietnam draft.

It played at 370 closed-circuit locations across the U.S. and seats at ringside were a staggering $150, though the upper reaches of the Garden could be had for $20. There were reports that ticket scalpers were getting up to $700, and business was brisk.

It wasn't just a fight, but a political and sociological litmus test. Ali was adored by many but despised by many more for his mouth, his refusal to be inducted in the Army and his Muslim religion. Frazier was his foil, a working man's heavyweight labelled an "Uncle Tom" by Ali because so many white Americans were on his side, cheering for him to win.

Meanwhile, about 10 American troops were still dying every day in Vietnam. The next month, some 200,000 people marched peacefully to the U.S. Capitol in Washington D.C., to protest a war that seemed to have no end. And, with a long, hot summer looming, occasional race riots continued to break out across a polarized country.

They fought for 15 rounds, furiously at times, with Frazier moving forward in a crouch throwing big left hooks while Ali shot out fast jabs and right hands to counter him coming in. But Ali's legs weren't what they were before his layoff, and he often had to stand his ground and fight when he previously was at his best sticking and moving.

Still, Ali had won the 14th round and seemed to be rallying when Frazier suddenly unleashed his best-left hook in a night filled with them. Shockingly, Ali was on the canvas. He managed somehow to get up and finish the round and the fight — but his fate that night had been decided.

Frazier would win a unanimous decision mostly because he simply refused to lose.

"Who's the champ? Who's the champ? Who's the champ?" Frazier crowed afterwards, though he hardly looked like a winner. While Ali's jaw was grotesquely swollen and he made a trip to the hospital for X-rays, Frazier's injuries were even more severe, and he would eventually require hospitalization.

But while Frazier left the ring as the undisputed heavyweight champion, Ali emerged a winner, too. He had fought magnificently and there was no shame in losing the way he did.

Ali would go on to reclaim his title two more times, including his knockout of George Foreman three years later in the iconic Rumble in the Jungle in Zaire that may have been his greatest fight. And he and Frazier would go on to make their rivalry a trilogy, meeting two more times, with Ali taking both fights. The third fight was the infamous Thrilla In Manila, which Ali said was the nearest thing to death he ever experienced — and a fight neither man ever fully recovered from.

Frazier died at the age of 67 in 2011, strapped for cash and still bitter about his treatment by Ali. Ali spent a good portion of his later life with his voice muted by Parkinson's disease. He died in 2016.

A half-century later they're gone. But their epic fight still lives on