In this corner: Joe Frazier, undefeated heavyweight champion of the world. His opponent: Muhammad Ali, also undefeated and trying to regain the crown he had lost on a technicality. The date was March 8, 1971, the first time Smokin’ Joe and the stingin’ butterfly had ever faced off. The sellout crowd at Madison Square Garden was about to see one of the great fights of the century: a 45- minute, 15-round seesaw of punishment that left both men seeking medical attention.

The fight, which appeared on closed-circuit TV, makes its network debut July 28 as part of NBC’s ”Greatest Fights Ever” series, preceded by a one-hour documentary that profiles the boxers and provides recent interviews with men from both corners of the ring.

”There was a lot of suspense attached to this first matchup,” says ”Fight Doctor” Ferdie Pacheco, part of Ali’s entourage until 1977 and a boxing commentator for the past 12 years. ”Ali had been stripped of his title and had been in exile for almost three years because of his refusal to enter the military draft. Frazier would not have had the title if Ali had been fighting. He had a cloud over his championship. There was also a cloud over Ali because he had been away from fighting and no one knew exactly what he had lost.”

Ali, then 29, was known as a dancer who floated away from dangerous punches gracefully. Frazier, 27, was considered a workhorse — a ”hooker” who used his massive strength to throw a battery of body punches to weaken opponents and then looked for that big hook to take them down.

But the favored Ali did not float like a butterfly; his legs were gone, and Frazier pounded him into the ropes. Yet Ali threw many saber-like jabs of his own. Except for rounds 4 (when Frazier looked ragged) and 11 (when Ali did), the fight was even. ”There was a feeling by the last round that something had to happen, and it did,” Pacheco says. ”Frazier threw a hook so hard he left his feet, and Ali went down.” The challenger got back up, but his four-count stay on the canvas (the first of his career) made the difference. The unanimous decision went to Frazier. Later, Ali said he had never seen a man as strong as Joe Frazier and hoped he never would again. Fortunately for fight fans, he changed his mind, and the two met twice more (Ali won both contests), continuing one of the most exciting rivalries in boxing history.