And the new WBA welterweight champion was crowned.
A crowd of 20,820 fans, the largest in the 10-year history of the Staples Center, watched in awe as Mosley scored a knockout at :23 of the ninth round, capping off a dominating display of hand speed that was surpassed only by the punishment of his power.
Margarito, whose fans clearly outnumbered Mosley's judging from the crowd's response, was able to survive after getting up from a knock down just before the bell rang to end the eighth round.
But Mosley quickly jumped on him again in the ninth, landing a left hook and right hand followed by more of the same until Margarito toppled to the canvas like a lumberjack's handiwork just as his corner threw in the towel.
Few of the so-called experts gave Mosley, 37, much chance of beating a champion seven years his junior and known as the "Tijuana Tornado," because of his relentless pressure. But the Pomona, Calif. native made it seem like it was June, 2000 all over again. That's when he decisioned Oscar De La Hoya for the WBC welterweight title in the first fight ever at Staples Center.
If the victory nine years ago made him a bona fide boxing super star, Mosley re-made himself Saturday night as the world's top 147-pounder.
"My preparation is what made this victory,'' Mosley said. "I trained so hard. I was so focused in the camp and in the ring tonight. I was so alert all the time,. Margarito is so powerful but he couldn't avoid my rhythm ."
Fighting an opponent noted for a granite chin, Mosley vowed that if anybody was going to be knocked out Saturday night that it was going to be him. He proved himself right.
"I knew I had him after the eighth,'' said Mosley, who used a leaping right uppercut to start the barrage that led to the first knock down. "I saw the end in the next round. My corner told me to go out with everything and finish him. And that's what I did."
Adding fuel to the fire before the HBO-televised bout was the controversy and potential scandal after Margarito was found to have a plaster-like substance inside both hand wraps. Initially, Nazim Richardson, Mosley's trainer, brought it to the attention of the California commission that Margarito appeared to have too much wrap on his hands.
After Margarito was prompted to re-wrap his hands, that's when the hard substance was discovered. The California commission confiscated the materials and plans to investigate. Richardson said Mosley should be given his full credit for beating Margarito, who was considered a solid favorite after his 11th-round TKO against previously unbeaten Miguel Cotto took the title in July.
"They said he was a monster and we conquered the monster, so don't take anything away from him,'' Richardson said. "The plan we had was to exploit the pressure that he brings. We made his pressure work against him. We killed him with it."
Mosley, having lost on a decision to Cotto in 2007, said he's up for a rematch. "Cotto or Margarito, it doesn't matter,'' he said.
Mosley's superior speed was apparent in the first round. He landed rapid double jabs followed by an overhand right and an uppercut that made Margarito also take note of his power.
Maintaining his aggressiveness in the second round, Mosley's quickness and slickness enabled him to land a n avalanche of solid punches but Margarito rallied late in the third round, landing a left hook that knocked Mosley off-balance to the delight of his fans.
As noteworthy as Mosley's offense was, Margarito showed remarkable toughness by weathering three and four hard shots to make his one count.
Several times, Margarito smiled and kept coming after taking the best Mosley had to offer. In the fifth round, Mosley visibly slowed his punch output and Margarito took advantage by staying busier, scoring well in the clenches and enjoying his best round to that point in the fight.
Mosley re-established his dominance in the sixth round, exploding with chopping rights that came too fast for Margarito to stand any chance of eluding them.
"It was frustrating,'' Margarito said. "I just couldn't avoid the right hand. I kept getting caught over and over. He has a lot of experience. I just couldn't put any punches together."