M uhammad Ali had just collapsed. Lying on his back in the center of the ring, surrounded by his cornermen, handlers, hangers-on and press, he was only visible as a flash of brilliant white through a thicket of legs. He had just won the undisputed heavyweight championship of the world.

The “Thrilla in Manila,” as Ali himself coined it, on 1 October 1975, is still regarded as the greatest and most brutal boxing match of all time 50 years on. A better bout, even, than Ali’s first matchup with Joe Frazier four years prior, which was billed as “The Fight of the Century” in New York City and saw Frazier’s hand raised after he dropped Ali at the start of the 15th and final round. Better too than their controversial Madison Square Garden rematch in January 1974, which ended with Ali the victor.

Despite the stale, stifling Philippine air – Frazier later said it may have been as hot as 120 degrees under the fiery overhead lights – both men wore robes to the fight. At the time, wrapped in a pale, long number with powder-blue trim, Ali looked angelic. Frazier contrasted in head-to-toe navy. Then they disrobed, and Ali stood there in his trademark Everlast shorts, pure white save for the black belt line and thin black racing stripes down each leg.

The shorts were Ali’s calling card. A symbol in satin. Because if you strip away the context, the stakes and everything else: Who wears white shorts to a fight?

The answer, of course, is someone who thinks they’re going to win, and to walk away looking pretty.

The white shorts – offered at Sotheby’s 27 March-10 April as part of Sports Week – represented Ali’s defiant, razor-edged optimism, borne not of naïveté but of ultimate self-knowledge and belief. White trunks tend to tell the story of a fight: A boxer could open his opponent’s brow with a punch then redeposit the blood on their opponent’s belt line with a crushing body blow. A boxer with a broken nose may paw at their face as they suck in heaving breaths through shattered sinuses. Running blood mixes with sweat and smears when two fighters clinch and clash and lean and shove. It just gets everywhere. And white trunks show it all.

Robert Lipsyte, the legendary former New York Times reporter who spent decades covering Ali, once told me that the boxer was “the most beautiful creature on the planet.” As a Louisville prodigy, Olympic gold medalist and young champion, Ali spent much of his career dancing through his opponents, hands low and out of sight, taunting them violently while claiming their health with stealthy shots from below his belt line. But by the time he fought Frazier in the Thrilla in Manila, he was different. By then he’d been through prison and was seen as a humanitarian hero for his opposition to the Vietnam War. Upon his return to the sport, he still held his hands low but didn’t dance as much. This Ali was willing to deliver punishment – and was unyielding in his ability and willingness to take it too.

With a billion people looking on (it was the first time a match was broadcast by continuous satellite signal, at 10 a.m. local time around the world), an official rang the opening bell. Then the legends crossed the mat and, as one, began their descent into hell. From the start of the match throughout, the men fought at a pace so frantic, with thudding exchanges so urgent, that at times Ali and Frazier seemed to envelop each other in a dark, tangled mass of fists, arms and elbows – save for those bright white trunks.

Joe Frazier was Muhammad Ali’s equal – as much as any man could be – and his opposite. In the ring, the taller Ali stood almost still, statuesque, fighting from range, while the shorter, industrious Frazier bobbed up and down, covering up and forcing his way inside. Frazier looked like a buoy as he bounced across the canvas, pushing Ali back against the ropes before uncorking thunderous body blows. Ali swayed and bent like a reed before emerging from behind his guard to snake long, straight one-twos almost exclusively to Frazier’s head.

They fought for 42 minutes. It felt like forever. A tragic irony is that the pace of the fight and the Philippine heat quickly sapped at the fighters’ legs and arms, draining either’s ability to finish the other. All they could throw were subconcussive blows. There wasn’t a single knockdown, but it was one of the most violent bouts of all time. And then, after 14 rounds, Frazier’s eye was shut. His trainer threw in the towel; he could witness no more.

Ali later explained, “It was like death. Closest thing to dying that I know of.”

But for such a bruising fight, it was bloodless. At the end, Ali’s white Everlast trunks looked pristine. This was tragic too, for there was no evidence of what each man took from the other. Perhaps if Ali’s shorts had been bloody, maybe the billion people looking on would’ve known and recoiled at what they were watching. Or maybe not.

The Joe Frazier who stepped into the ring that muggy morning never left it. His vision was compromised for the rest of his life, and the 31-year-old only fought twice more before retiring. The “Thrilla in Manila” is seen not just as the first day of the slow death of Muhammad Ali the fighter, but as the first day of the slow demise of Muhammad Ali the man. “We went to Manila as champions, Joe and me,” Ali later said, “and we came back as old men.” Ali boxed for six more years, retaining, then losing, then recapturing heavyweight titles. But he danced less and less.

In 1984, just three years after retiring from boxing, he was diagnosed with Parkinson’s. He passed at the age of 74, after three decades of battling the disease, on 3 June 2016. But by 1 October 1975 in Manila, Ali was already something more, something different, than just a man. He was a beacon, a blinding light in a sea of dreams. Standing there, back straight, hands low, in those unmarred white trunks, Muhammad Ali was the most beautiful creature on the planet, and he wanted everyone to see.