In the table from reputable boxing website BoxRec, the retired 50-0 champ is ranked far ahead of second-placed Manny Pacquiao. Mayweather, 42, of Michigan, has never lost a professional fight in his 21-year career, and his place at the top of the rankings is another another punch at his ferocious opponent from the Philippines. Mayweather's record is unblemished since he moved up to welterweight to face Marcos Maidana in April 2014. He defended his title with convincing victories over Ricky Hatton and Oscar De La Hoya in 2009 and 2007 respectively. Maidana was the only opponent who gave Mayweather any real trouble during this period but even so, his winning streak is still intact. Mayweather announced his retirement on Instagram after his ninth win via knockout/TKO. He said he's moving down to light heavyweight for his next contest to avoid getting beaten up by boxers of higher weight classes. "My body needs a break," he said. "I'm going to take one year off and see what happens." Mayweather won his first seven fights by way of knockout/TKO. His sole defeat came when he was caught by a left hook from Miguel Cotto in 2010 which caused him to lose his belt. After coming back from that setback, he went on to defend his title against Hatton and De La Hoya twice each.