By Mark Lamport-Stokes
Having already established himself as one of the best offensive fighters of all time, Pacquiao outclassed Margarito with his lightning hand speed and precise power punching to improve his career record to 52-3-2 with 38 knockouts.
"It was a really hard fight, the hardest fight in my boxing career," Pacquiao told reporters after winning his 13th consecutive bout since losing to Erik Morales in Las Vegas in March 2005.
"He's strong. I never expected him to be as strong as he was. He's a very tough fighter. I can't believe he took all those punches."
Despite being outweighed by 17 pounds, Pacquiao blended raw power with speed in front of a crowd of 41,734 to deliver a spectacular performance against an opponent who was also four-and-a-half inches taller.
The pride of the Philippines, who had never previously fought above welterweight, dominated the official ringside statistics, landing 474 power punches compared to Margarito's 229.
At one point during the 11th round, Pacquiao looked across at referee Laurence Cole and asked him to stop the fight.
"In the 12th round I wasn't looking for a knockout. I take it easy because my trainer told me to take it easy and just be careful."
Pacquiao, fighting for the first time since winning a seat in his country's national congress earlier this year, gained one-sided verdicts from all three judges -- 120-109, 118-110 and 119-109.
"We didn't lose a round," said Pacquiao's trainer, Freddie Roach. "Manny fought a great fight tonight and Margarito showed a lot of heart. He is very resilient. I thought for sure he would quit."
Pacquiao's initial concern after the fight was the health of his mother, who according to promoter Bob Arum had "suffered an anxiety attack" while watching her son from ringside.
"She's okay now, she's okay," Pacquiao told reporters before holding his post-fight news conference.
Asked whether he had considered retiring before the end of the 12th round, Margarito replied: "No, no way. I'm a Mexican and we fight until the end. This time I failed Mexico but we will fight to the end."
The controversial Mexican was welcomed by a mixture of cheers and jeers when he first made his way toward the ring set up in the state-of-the-art home venue for the Dallas Cowboys NFL team.
Margarito and his trainer Javier Capetillo were banned for a year after plaster-like bandage wraps were found in the fighter's gloves before the Mosley fight, prompting Roach to monitor the Mexican's hand-wrapping on Saturday.
(Editing by John O'Brien)