San Diego witnessed one of the most remarkable upsets in heavyweight history on 31 March 1973, when Ken Norton handed Muhammad Ali only the second defeat of his career. In front of 11,884 spectators at the Sports Arena, Norton defied the bookmakers, who had made Ali a heavy favourite, and walked away with the NABF heavyweight championship on a split decision.

Ali entered the ring in a dazzling rhinestone robe gifted by Elvis Presley, a garment that would never again make an appearance. The bout, carried live on ABC, was meant to showcase Ali rebuilding momentum after his first professional loss to Joe Frazier. Instead, it produced a new name in the sport and the beginning of a fierce rivalry.

From the opening bell, Norton’s awkward style unsettled the former champion. Crossing his arms defensively and shooting jabs from unusual angles, the ex-Marine pressed forward with determination. Ali looked sluggish, spending long spells near the ropes, where he absorbed body shots and struggled to find his rhythm. By the end of twelve rounds, the scorecards told the story: Judge Hal Rickards favoured Norton 5–4, referee Frank Rustich gave Norton the edge 7–5, while Judge Fred Hayes had Ali ahead 6–5. The split decision went to the San Diego man, sparking debate throughout the boxing world.

Statistics underline the scale of the performance. Norton landed 233 punches at 43 percent accuracy, compared with Ali’s 171 at 26 percent. In power shots, Norton held a commanding lead, 124 to 78. He outscored Ali in eight of the twelve rounds, steadily building confidence as the minutes ticked away.

The drama did not end at the final bell. Ali left the ring nursing a serious injury—his jaw fractured in several places. Accounts differed as to when the break occurred, with Ali’s trainer Angelo Dundee believing it happened early, while Norton’s camp suggested much later. Surgeons later described the damage as severe, requiring wiring to hold the bone in place.

Despite the setback, Ali showed dignity in defeat, shaking Norton’s hand before heading to hospital. Norton, meanwhile, proved gracious in victory, visiting his opponent afterwards in a gesture that laid the groundwork for mutual respect.

Financially, the night was significant too. The gate produced $240,792, with Ali guaranteed $210,000. Norton, earning $50,000, received the biggest purse of his career by a wide margin.

The San Diego triumph established Norton as more than a sparring partner to Joe Frazier. It cemented him as a force in the heavyweight division and marked the opening chapter of a trilogy that would become one of boxing’s defining rivalries.