A blood-splattered Juan Manuel Marquez survived a broken nose and standing eight count to beat Manny Pacquiao with a stunning knockout at the MGM Grand in Las Vegas.
The 39-year-old Mexican connected with a straight right hand to Pacquiao's chin in the final second of the sixth round to knock the Filipino clean out.
Marquez had Pacquiao on the canvas as early as the third round, when a straight right counter punch dropped the 33-year-old Filipino - the first knockdown he had scored against him in four contests.
However, Marquez failed to capitalise on the early breakthrough and reverted to his trademark defensive style.
Manny Pacquiao lays face down on the mat after being knocked out in the sixth round as Juan Manuel Marquez celebrates during their welterweight bout at the MGM Grand Garden Arena on Sunday in Las Vegas. (Photo by AFP)
Pacquiao regrouped and went on the attack, releasing a flurry of combinations.
Marquez survived a standing eight count in the fifth round following a straight right from Pacquiao.
Again, Pacquiao went on the attack, with Marquez suffering a cut above his right eye and what appeared to be a broken nose.
With Pacquiao in the ascendancy and seemingly taking control of the fight at the end of the sixth, Marquez summoned a tremendous counter punch that may spell the end of the Filipino's glorious career.
Marquez climbed the ropes with his right hand raised in victory, his own blood splattered across his chest from the earlier damage inflicted by Pacquiao.
Although he spent around one minute lying on the canvas out cold, initial concern for Pacquiao's health subsided when the Filipino regained consciousness with a wry smile.
The fourth contest between the two rivals is the first to provide a truly conclusive result in the eyes of many boxing observers, following a draw and two controversial wins for Pacquiao.
The result now leaves a much touted contest between Pacquiao and Floyd Mayweather Junior in doubt.