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

Manny Pacquiao, from the Philippines, lies on the canvas as referee Kenny Bayless kneels nearby after being knocked out by Juan Manuel Marquez, from Mexico, in the sixth round of their WBO world welterweight fight Sunday, Dec. 9, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, celebrates his sixth round knockout victory over Manny Pacquiao, from the Philippines, in their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, right, celebrates after knocking 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. Referee Kenny Bayless tends to Pacquiao. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, left, and Manny Pacquiao, from the Philippines, trade blows during their WBO world welterweight fight Sunday, Dec. 9, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Manny Pacquiao, from the Philippines, lifts his trunks after being knocked down in the third round of his WBO world welterweight fight against Juan Manuel Marquez, from Mexico, Saturday, Dec. 8, 2012, in Las Vegas. Referee Kenny Bayless looks on at left. (AP Photo/Julie Jacobson)

Juan Manuel Marquez, from Mexico, left, knocks down Manny Pacquiao, from the Philippines, in the third round of their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, right, knocks out Manny Pacquiao, from the Philippines, in the sixth round of their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, right, knocks out Manny Pacquiao, from the Philippines, in the sixth round of their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, right, lands a right to the head of Manny Pacquiao, from the Philippines, during their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. Marquez won by a knockout. (AP Photo/Julie Jacobson)