Las Vegas (CNN) -- Manny Pacquiao continued his conquest of the boxing world Saturday night when he defeated "Sugar" Shane Mosley in Las Vegas.
The Filipino fighter retained his World Boxing Organization welterweight title at the MGM Grand Hotel and Casino. Pacquiao defeated Mosley by a unanimous decision, 119-108, 120-108, 120-107 after 12 rounds.
Mosley came into the fight as a former three-time world champion.
But the 39-year-old American was a clear underdog, in part from his having won only two of his past five fights. He endured grueling defeats to Floyd Mayweather Jr., and Miguel Cotto and a draw with Sergio Mora.
Mosley put up a brave showing but was always on the back foot against Pacquiao, who knocked him down in the third round, the first time he had been on the canvas in nine years.
"After the first knockdown I felt I had him and I got him and that I could finish him," Pacquiao told gathered reporters after the fight.
"But the next round I have a problem with my left foot it is tight.
"I told my coach to press my legs because they are too tight."
Bothered by the cramp, Pacquiao was briefly floored himself in the 10th, but said the referee had apologized to him after the fight for a wrong decision in awarding the knockdown.
The main reason Pacquiao, 32, was the heavy favorite was his own dominance of late. He is the first boxer ever to capture 10 world titles in eight weight divisions -- from flyweight (for boxers between 108 and 112 pounds) up to super welterweight (148 to 154 pounds).
The Ring magazine, among other publications, ranks Pacquiao as the world's best pound-for-pound boxer. Entering Saturday night, he'd won 14 straight fights and compiled a professional record of 52 wins, three losses and two draws -- with 38 of those winning decisions coming by knockout.
His exemplary record, obvious skill and international appeal -- especially in southeast Asia -- have helped make Pacquiao one of the world's most recognizable and admired boxers.
But the native of General Santos city in the Philippines has proven he's more than just a fighter.
Last year, he was elected as a federal congressman in the Philippines.
Pacquiao has also dabbled in American politics, with Senate Majority Leader Harry Reid crediting the Filipino's appearance at a last-minute rally in 2010 for helping seal his own election victory.
He is also an aspiring singer, having appeared on U.S. shows such as "Jimmy Kimmel Live!" and released albums in Tagalog and English.
Given the diversity and time-consuming nature of Pacquiao's interests, trainer Freddie Roach has been among those questioning how much longer the fighter known as "Pacman" will continue to fight in the ring.
One of the biggest lingering questions involving Pacquiao is whether a much-touted showdown with Mayweather ever comes to fruition.
Negotiations last year broke down amid accusations (including Mayweather's unverified claim Pacquiao used performance-enhancing drugs), recriminations and legal threats. Negotiations remain in limbo after Mayweather's arrests on suspicion of battery and larceny.
CNN's Leif Coorlim contributed to this report.