Manny Pacquiao knocked down Miguel Cotto twice and turned his face into a bloody mess before finally stopping him 55 seconds into the 12th round Saturday to win his seventh title in seven weight classes.

The Filipino star used his blazing speed and power from both hands to cement his stature as the best pound-for-pound boxer in the world.

Cotto took such a beating that his face was a river of red from the fury of Pacquiao's punches but he refused to quit even as his corner tried to throw in the towel after the 11th round.

The fight was billed as a 145-pound classic, and in the early rounds it didn't disappoint. The two went after each other with a vengeance and Cotto more than held his own as they traded punches in the centre of the ring.

Big left hand

Pacquiao dropped Cotto with a right hand early in the third round, but he wasn't badly hurt and came back to finish the round strong. But after Pacquiao put Cotto on the canvas with a big left hand as Cotto was advancing forward late in the fourth round, the Puerto Rican was never the same again.

"Our plan was not to hurry but to take our time," Pacquiao said. "It was a hard fight tonight and I needed time to test his power."

Cotto fought gamely but in the later rounds he was just trying to survive as blood flowed down his face and Pacquiao kept coming after him relentlessly. In the 12th, Cotto went back out to take even more punishment before a final flurry along the ropes prompted referee Kenny Bayless to stop the fight.

Cotto's wife and child, who were at ringside, left after the ninth round, unable to watch the beating any longer. They later accompanied him to a local hospital for a post-fight examination.

"My health comes first. I just want to make sure I'm fine, but I feel great. I'm swollen but that's all," Cotto said.

Cotto's face was swollen, blood was flowing from his nose and his cuts, and he simply couldn't stop Pacquiao from bouncing inside and throwing both hands at will.

Trademark fashion

"I didn't know from where the punches were coming," Cotto said. "Manny Pacquiao is one of the best boxers I ever fought."

Pacquiao, coming off spectacular wins over Oscar De La Hoya and Ricky Hatton, added another one against Cotto, who had lost only once and held the WBO version of the welterweight title. Pacquiao did it in trademark fashion, throwing punches in flurries and from all angles until Cotto began to slow down, and then pursuing him relentlessly until the fight finally ended.

The fight will likely set up an even bigger fight against Floyd Mayweather Jr, and many in the capacity crowd at the MGM Grand arena began chanting "We want Floyd! We want Floyd" after the fight ended.

"I want to see him fight Mayweather," trainer Freddie Roach said.

Second thoughts

Mayweather may have second thoughts after Pacquiao did what no fighter has done before and win a belt in a seventh weight class. More impressive, though, is how he has fought, dismantling opponents despite moving up consistently in weight.

The welterweight ranks will be the last ones Pacquiao conquers, though. He said he will not move up any more in weight.

"This is the last weight division for me," Pacquiao said. "It's history for me and more importantly a Filipino did it."

Pacquiao was credited with landing almost twice as many punches - 336-172 - as Cotto. He earned a minimum US$13 million for the win, while Cotto got US$7 million

Pacquiao was favoured, largely off his last two performances in which he forced De La Hoya to quit on his stool and then knocked out Hatton with a huge left hook in the second round.