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Manny Pacquiao is knocked down in the third round while taking on Juan Manuel Marquez during their welterweight bout at the MGM Grand Garden Arena on December 8, 2012 in Las Vegas, Nevada. (Photo by Al Bello/Getty Images)

Referee Kenny Bayless, left, directs Juan Manuel Marquez, right, to a corner as Manny Pacquiao sits on the mat after being knocked down by Marquez in the third round during a welterweight fight, Saturday, Dec. 8, 2012, in Las Vegas. Marquez knocked out Pacquiao in the sixth round to win their fourth bout. (AP Photo/Julie Jacobson)

Manny Pacquiao, left, and Juan Manuel Marquez battle during their welterweight fight on December 8, 2012, at the MGM Grand Garden in Las Vegas, Nevada. Marquez knocked out Pacquiao in the 6th round. JOHN GURZINSKI/AFP/Getty Images

Former Republican U.S. presidential candidate Mitt Romney waits for the start of a welterweight bout between Manny Pacquiao of the Philippines and Juan Manuel Marquez of Mexico at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Manny Pacquiao prays in the ring before taking on Juan Manuel Marquez during their welterweight bout at the MGM Grand Garden Arena on December 8, 2012 in Las Vegas, Nevada. (Photo by Al Bello/Getty Images)

Juan Manuel Marquez, left, of Mexico connects on Manny Pacquiao of the Philippines during their welterweight fight at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Juan Manuel Marquez, left, of Mexico takes a punch from Manny Pacquiao of the Philippines during their welterweight fight at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. Marquez went on to win with a sixth-round knockout. REUTERS/Steve Marcus

Juan Manuel Marquez, left, of Mexico punches at Manny Pacquiao of the Philippines during their welterweight fight at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Manny Pacquiao of the Philippines is treated in his corner between rounds during his welterweight fight against Juan Manuel Marquez of Mexico at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. Marquez sensationally knocked out Pacquiao in the sixth round of their non-title welterweight bout on Saturday, getting his first win over the Filipino in four attempts. REUTERS/Steve Marcus

Filipinos react after seeing Filipino boxing hero Manny Pacquiao was knocked out by Mexican Juan Manual Marquez during a live TV broadcast at a multi-purpose hall in suburban Paranaque, south of Manila, Philippines on Sunday, Dec. 9, 2012. Many Filipinos were stunned by Pacquiaoís knockout defeat to Marquez, dampening the spirit of a nation battered recently by a powerful typhoon. (AP Photo/Aaron Favila)

Juan Manuel Marquez of Mexico bleeds from a cut on his face during his welterweight fight against Manny Pacquiao of the Philippines at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Manny Pacquiao, left, and Juan Manuel Marquez exchange blows during their welterweight bout at the MGM Grand Garden Arena on December 8, 2012 in Las Vegas, Nevada. (Photo by Al Bello/Getty Images)

Manny Pacquiao lays face down on the mat after being knocked out in the sixth round by Juan Manuel Marquez during their welterweight bout at the MGM Grand Garden Arena on December 8, 2012 in Las Vegas, Nevada. (Photo by Al Bello/Getty Images)

Juan Manuel Marquez of Mexico celebrates as referee Kenny Bayless signals an end to the welterweight fight after Marquez knocked out Manny Pacquiao of the Philippines in the sixth round at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Referee Kenny Bayless, left, calls the fight as Juan Manuel Marquez, from Mexico, right, celebrates after he knocked out Manny Pacquiao, from the Philippines, lower left, in the sixth round of their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Hands reach in ringside to support the head of Manny Pacquiao after he was knocked out by Juan Manuel Marquez on December 8, 2012, at the MGM Grand Garden in Las Vegas, Nevada. JOHN GURZINSKI/AFP/Getty Images

Juan Manuel Marquez of Mexico celebrates his 6th round knock out victory over Manny Pacquiao of the Philippines during their welterweight fight at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. REUTERS/Steve Marcus

Juan Manuel Marquez of Mexico celebrates his 6th round knock out victory over Manny Pacquiao of the Philippines during their welterweight fight at the MGM Grand Garden Arena in Las Vegas, Nevada December 8, 2012. Boxing promoter Fernando Beltran is at left. REUTERS/Steve Marcus

Juan Marquez speaks during a press conference after his 6th round knockout victory over Manny Pacquiao, Saturday, Dec. 8, 2012, at The MGM Grand Garden Arena in Las Vegas. (AP Photo/Eric Jamison)