LOS ANGELES -- Besieged by outside-the-ring problems, "Sugar" Shane Mosley never let them bother him, at least publicly.
Instead, he carried himself with a quiet confidence throughout the buildup to his fight with Antonio Margarito.
And when they finally got into the ring Saturday at the Staples Center, with a record crowd of 20,820 going crazy -- and mostly cheering for Margarito -- it seemed as though Mosley let whatever frustration that may have built up inside of him out on Margarito.
It was a thrashing.
There was a knockdown in the eighth round.
And a knockout 43 seconds into the ninth round, a round in which the Sugarman closed the show by outlanding Margarito a staggering 21-0.
The victory, in which Mosley, from nearby Pomona, regained the welterweight championship, was validation that he's still great, even at 37.
Outside the ring, Mosley -- a former lightweight champ, now a two-time welterweight champ and unified junior middleweight champion -- has had a lot of problems in recent months. He's continually been dogged by his involvement in the BALCO steroids scandal and his admission that he had used substances given to him by disgraced BALCO boss Victor Conte before his second win against Oscar De La Hoya in September 2003. They turned out to be designer steroids "the clear" and "the cream." He also admitted to being injected with EPO, a blood oxygen enhancer.
There is also an ongoing defamation lawsuit with Conte.
And a change of trainers as Mosley fired his father, Jack, for the second time in his career and replaced him with Nazim Richardson.
And divorce proceedings with his wife, Jin, the mother of three of his children. In fact, Mosley broke training camp in Big Bear, Calif., recently to come to Los Angeles to finalize their settlement in mediation.
None of which seemed to bother Mosley (46-5, 39 KOs).
Instead, he turned back the clock to the previous greatest night of his career. That was in June 2000, when he scored his career-defining first victory against De La Hoya to win the welterweight championship for the first time.
That also happened to be the first boxing card ever held at the Staples Center.
All these years later, Mosley is back on top in the same building that first made him so famous.
"It was my strategy, my focus and my game plan. I had a good coach," Mosley said, thinking of all the reasons he was able to pull the upset against Margarito, who had shot to the top of the sport on the strength of his 11th-round knockout of Miguel Cotto last summer. "I knew it was a tough fight, but it was a great plan. It was my left hook. I caught [Fernando] Vargas with it and [Ricardo] Mayorga with it. He's a very tough fighter and he had a lot of endurance."
Mosley, an underdog perhaps in part because he had suffered a close decision loss to Cotto in November 2007, was way faster than Margarito. And he seemed to also land much heavier blows as he pressured Margarito, who is normally the pressure fighter, throughout the fight.
"When you have a great game plan and an excellent athlete, then everything works out really well," Richardson said. "[Margarito] said he was a monster and we conquered the monster. Don't take anything away from him. I exploited that his pressure could work against him. We turned his pressure against him and killed him with it."
Clearly ahead during what was an entertaining fight, Mosley did serious damage in the eighth round.
Mosley was landing huge shots when he finally knocked the usually iron-chinned Margarito down, sending him into the ropes with left hands and down on the end of hard right hands.
Margarito (37-6, 27 KOs) went down face-first and was smiling when he rose.
He knew he had been nailed and was in deep trouble.
In the ninth, he had nothing left. Mosley was teeing off on him in his corner, and as Margarito fell again, referee Raul Caiz was moving in to stop the fight at the same time Margarito's corner threw in the towel.
It was as comprehensive a victory as Mosley, who like Margarito earned $2.4 million, could have authored.
"I prepared very hard. I trained hard so I was focused and I was always alert during the fight," Mosley said. "He was very powerful but he couldn't resist my rhythm."
Margarito trainer Javier Capetillo knew something was wrong with his man from the start.
"Something happened in the first round," he said. "We were too slow. I didn't think he was reacting properly. It was frustrating to watch because he kept getting caught with overhand rights."
Perhaps Margarito, 30, was out of sorts because he was forced to have his hands rewrapped before the fight after an illegal substance was discovered. Whatever it was, he took his beating like a man.
Dejected afterward, Margarito said, "I feel OK. I was just getting caught over and over."
And over and over and over.
Dan Rafael is the boxing writer for ESPN.com.