Manny Pacquiao, widely considered the world's best pound-for-pound fighter, is defending his WBO welterweight championship against "Sugar" Shane Mosley on Saturday at the MGM Grand Garden Arena in Las Vegas. The fight marks Pacquiao's second defense of the 147-pound title he won from Miguel Cotto in 2009. The first came against Josh Clottey in March 2010, after which Pacquiao moved up and beat Antonio Margarito for a vacant super welterweight title last November. That victory made Pacquiao the first boxer to capture world championships in eight different weight classes (from 112 to 154).