A bloodied Juan Manuel Marquez rallied to knock out eight division champ Manny Pacquiao with one second left in the sixth round and win the fourth fight of their epic boxing rivalry.
The 39-year-old Marquez, who suffered a broken nose and possible concussion, dropped Pacquiao face first to the canvas, giving him his first victory over the Filipino superstar.
Marquez knocked Pacquiao down in the third round then ended the fight with a savage overhand right that hit Pacquiao flush, sending him down hard.
"I feel great that I leave no doubt in the way I got this victory over Manny," Marquez said. "I was counter punching him. He was throwing a lot of punches but he was missing and so I would try to counter punch.
"The right hand I got under his guard. I threw the right when he missed a punch on me."
Pacquiao, who suffered his second consecutive loss, landed under the ropes and lay there for a couple of minutes before being helped up and back to his corner.
"I got hit with a punch I didn't see," said Pacquiao before being taken to the nearby University Medical Center hospital for treatment. "I thought I was getting him in the last couple of rounds but I got hit by a strong punch. I did not expect that punch."
Pacquiao did not attend the post-fight news conference. His camp said he was undergoing scans of his head area and other medical tests.
The shocking ending stunned the crowd of 16,348 at the MGM Grand Garden arena as Marquez had held his own in their first three fights but had never even knocked down Pacquiao until Saturday night.
Pacquiao dismissed talk of retirement and said he would like to fight Marquez again.
"I am going to rest and come back to fight. I would go for a fifth," he said.
There was shock and sadness in the Philippines, where the country came to a stop to watch their idol in action.
Marquez said he is not thinking about a rematch at the moment.
"I think this fight was one of my best victories absolutely," Marquez said. "Right now in my future I don't know what is coming."
Pacquiao, who was a three-to-one favorite on Friday, dropped to 54-5-2 with 38 knockouts. Pacquiao weighed in at the division's 147-pound limit (66.67kg) while Marquez, who improved to 55-6-1 with 40 knockouts, stepped on the scale at 143 pounds (64.86kg).
The fighters set a blistering pace, making it look unlikely this fight would go the distance as their three previous fights had.
"He is not an easy opponent," Pacquiao said. "I was just starting to feel confident and then I got careless."
Pacquiao was eager to redeem himself after suffering a controversial defeat in his most recent fight to Tim Bradley. He was also tired of Marquez blaming his failure to win in their three previous fights on biased judging.
Marquez claims he won all three earlier fights -- although two were scored in favor of Pacquiao and one ended in a draw.
This time, four division champion Marquez left no doubt, showing he was willing to go toe-to-toe with Pacquiao even after getting knocked down in the fifth round.
He had knocked Pacquiao down Saturday for the first time in 39 rounds between them in the third round with a right hook over the top.
"It was a good shot, but I was able to come back," Pacquiao said of the third-round knockdown.
Indeed, Pacquiao kept coming and Marquez appeared to be heading to his third defeat to Pacquiao after Marquez was bloodied and knocked down in the fifth.
Pacquiao came out attacking from the opening bell throwing lefts over the top of Marquez's gloves.
Pacquiao was the aggressor early, landing a solid left halfway through the second that jolted Marquez, stopping him in his tracks.
By the time the sixth round started Marquez looked a bloody mess, bleeding from a gash over his nose and from the mouth.
Both the third and fourth rounds ended with the boxers slugging it out in the center of the ring in a fight that at times resembled more of a wild street brawl.
"After the first knockdown Manny came back and he was in charge," said Pacquiao's trainer Freddie Roach. "But he got a little too careless."
Spectators got their money's worth as the fight more than lived up to its pre-fight hype.
Republican presidential nominee Mitt Romney sat in the front row to watch the fight. Romney was a guest of Nevada boxing chairman Bill Brady. Romney also chatted at ringside with NBA star Metta World Peace of the Los Angeles Lakers and rapper Curtis '50 Cent' Jackson.
Magic Johnson, Steven Seagal and Mike Tyson were also watching the fight at ringside.
Much of the pre-fight buzz centered around the judging after Marquez claimed he had been cheated out of previous wins.
In the end, Marquez took matters into his own hands making sure referee Kenny Bayless and the three judges -- Adalaide Byrd, Steve Weisfeld and John Keane -- weren't going to decide it.