Manny Pacquiao - Juan Manuel Marquez IV

Manny Pacquiao was dropped by a vicious right hand by longtime rival Juan Manuel Marquez in the sixth round as the two fought for the

fourth time at the MGM Grand Garden Arena in Las Vegas, Nev. on Saturday, Dec. 8, 2012.

Manny Pacquiao

LAS VEGAS, NV - DECEMBER 08: 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

LAS VEGAS, NV - DECEMBER 08: (R-L) Manny Pacquiao knocks down Juan Manuel Marquez in the fifth round 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, 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)

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)

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. Referee Kenny Bayless looks on at left rear. (AP Photo/Julie Jacobson)

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. Referee Kenny Bayless looks on at left rear. (AP Photo/Julie Jacobson)

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

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

Referee Kenny Bayless calls the fight as he kneels over Manny Pacquiao, from the Philippines, after he was knocked out by Juan Manuel Marquez, from Mexico, during their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Julie Jacobson)

Referee Kenny Bayless calls the fight as he kneels over Manny Pacquiao, from the Philippines, after he was knocked out by Juan Manuel Marquez, from Mexico, during their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Julie Jacobson)

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)

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)

A Filipino boy watches Filipino boxing hero Manny Pacquiao lying on the mat after he 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 Pacquiao’s knockout defeat to Marquez, dampening the spirit of a nation battered recently by a powerful typhoon. (AP Photo/Aaron Favila)

Juan Manuel Marquez, from Mexico celebrates his win over Manny Pacquiao in their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Julie Jacobson)

Juan Manuel Marquez, from Mexico celebrates his win over Manny Pacquiao in their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Julie Jacobson)

Juan Manuel Marquez, from Mexico, left, celebrates his win over Manny Pacquiao in their WBO world welterweight fight Saturday, Dec. 8, 2012, in Las Vegas. (AP Photo/Eric Jamison)

Juan Manuel Marquez, from Mexico, left, celebrates his win over Manny Pacquiao in their WBO world welterweight fight Saturday, Dec. 8, 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/Julie Jacobson)

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/Julie Jacobson)