LOS ANGELES -- Shane Mosley dominated from start to finish, knocking out Antonio Margarito for the first time in his career in the ninth round Saturday night to win the WBA welterweight title in a stunning upset.
Margarito was coming off an impressive victory over previously unbeaten Miguel Cotto six months ago, and boxing experts had tabbed the 30-year-old slugger one of the top pound-for-pound fighters.
But Mosley must not have been paying attention.
Despite his advancing age, the 37-year-old Mosley used his superior quickness from the beginning, and Margarito never was able to display the power and fortitude he showed against Cotto.
"It was my strategy, my focus, my game plan," Mosley said when asked what won the fight. "It was a tough fight, but it was a great plan. It was my left hook. I caught [Fernando] Vargas with it, I caught [Ricardo] Mayorga with it.
"He's a tough fighter, he had a lot of endurance. I prepared very hard, I trained hard. He was very powerful, but he couldn't resist my rhythm."
Mosley brought in Nazim Richardson to train him for this fight, replacing his father, Jack. That move worked to perfection.
"When you have a great game plan and an excellent athlete, then everything works out very well," Richardson said.
The bout was held before an announced crowd of 20,820 -- largest to attend a sporting event at Staples Center since it opened in October 1999. The fans were clearly pro-Margarito despite the fact that Mosley grew up in suburban Pomona, but it meant little once the bout began.
"I feel OK. I was just getting caught over and over," said Margarito, who was taken to a hospital to be checked out.
Margarito, of Tijuana, Mexico, didn't win a single round on one judge's scorecard, one on another and two on the third before the ninth. The Associated Press had Mosley every round but one.
Mosley, who weighed the maximum 147 pounds, raised his record to 46-5 with 39 knockouts. Margarito, known as the "Tijuana Tornado," weighed 145.8 pounds. He dropped to 37-6 with 27 knockouts.
Both fighters earned around $2.4 million.
While the 30-year-old Margarito was at his best in beating Cotto, Mosley certainly wasn't in his last outing, a 12th-round knockout of Mayorga four months ago at Home Depot Center in nearby Carson. Mosley was ahead on two of the three judges' scorecards when the end came in that fight.
Mosley was far better against Margarito. Mosley lost a close but unanimous 12-round decision to Cotto before that, on Nov. 10, 2007, and said afterward he'd love another shot at Cotto.
Before the fight, ESPN.com's Dan Rafael reported Margarito had to have his hands rewrapped after a complaint by Richardson during his pre-fight inspection.
Stephen Espinoza, attorney for Golden Boy Promotions, said he was told by Dean Lohuis, co-executive director of the California State Athletic Commission, that a plaster-like substance was found under both of Margarito's hand wraps and had been bagged as evidence.
None of that mattered once the action began. Mosley landed 178 punches to 108 for Margarito and 118 power punches to Margarito's 78.
Margarito fans at ringside, perhaps understanding their fighter was in trouble, began a pleading "Margarito, Margarito" chant as the eighth round began, and the Mexican boxer's corner came to life when he landed his most solid blows of the fight to that point.
But Mosley staggered the champion late in the round, and floored him with a barrage of punches as the round ended. Margarito wobbled to his feet to beat the count to 10, but looked like a beaten man as he sat in his corner.
Mosley continued to force the action in the ninth, and finally Margarito's corner threw in the towel when the fighter was unable to defend himself. Mosley landed 18 power punches and 21 overall to none for Margarito in the final round.
"Something happened in the first round," said Javier Capetillo, Margarito's trainer. "We were too slow. I didn't think he was reacting properly. It was frustrating to watch because he kept getting hit by overhand rights."
The fans began a "Margarito, Margarito" chant in the opening seconds of the first round, and the fighters were slugging it out toe-to-toe by the middle of the round. Mosley got what appeared to be some good shots in, but Margarito responded with a smile.
The crowd roared when the fighters traded solid punches early in the third round, and Margarito again flashed a grin after Mosley nailed him with several blows, none of which seemed to do much damage. But Mosley, using his superior quickness, was connecting more often.
Margarito appeared to be picking up steam in the fourth round, but again, Mosley caught him with several punches, and Margarito didn't respond with a smile until Mosley nailed him with a right hand as the round ended. That grin appeared to be one of acknowledgment.
Mosley was fighting at Staples Center for the second time. He won a 12-round split decision over Oscar De La Hoya on June 17, 2000 in the first boxing match held at the downtown Los Angeles arena.
On the undercard, Robert Guerrero of Gilroy, Calif., stopped Edel Ruiz of Los Mochis, Mexico just 27 seconds into their 10-round featherweight bout.
Guerrero used a single left hand punch to the body to floor Ruiz, who spent a couple minutes on his hands and knees before being helped to his feet.
Guerrero (23-1-1, 16 knockouts), a two-time former featherweight champion, hadn't fought in nearly 11 months while working to leave promoter Dan Goossen. Golden Boy Promotions signed Guerrero shortly after an arbitrator resolved the dispute last month.
The 25-year-old Guerrero, who vacated his IBF featherweight title during his layoff in a plan to move up to 130-pound fights, weighed 129.5 pounds. Golden Boy executives have said they hope to get a him super featherweight title shot this year.
Ruiz lost for the eighth time in his last 11 fights to fall to 29-22-5. He weighed 129.7 pounds.
The program was promoted by Top Rank and Golden Boy Promotions.