Juan Manuel Marquez produced a huge right hand to knock Manny Pacquiao out and win a devastating victory in the latest chapter of one of the sport's most compelling rivalries.
Both fighters had been sent sprawling in an action-packed bout in Las Vegas, and it was Pacquiao who appeared to be on top before Marquez produced a brutal blow right at the end of the sixth round to seal the win he craved so badly.
The win may bring 39-year-old Marquez no titles, but for the Mexican it ended years of frustration as he vanquished his rival at the fourth attempt.
Their previous three encounters have not been short of controversy with decisions disputed, but there was no doubt about this one.
After two cagey rounds, it was Marquez who landed the first telling blow in the third.
A big right-hander sent Pacquiao to the canvas and, though he bounced straight back up again, it was clear the Filipino was rattled.
A high-octane and even fourth followed, but in the fifth it was Pacquiao who stepped up a gear, landing a big left jab on Marquez, who touched the canvas with his glove.
With Marquez cut and hurting, the 33-year-old scented blood and pressed forward in the sixth.
But in his haste to finish off Marquez he left himself open and the Mexican produced a thundering counter-punch which left Pacquiao face down on the canvas.