The Filipino southpaw stopped his bigger opponent 55 seconds into the 12th and final round at the MGM Grand Garden Arena to land a seventh world title in an unprecedented seventh weight class.
Pacquiao twice knocked the Puerto Rican to the canvas in the earlier rounds before referee Kenny Bayless ended the fight after Pacquiao had pummelled his opponent with a flurry of combinations against the ropes.
“Our plan was not to hurry but to take our time,” a beaming Pacquiao said in a ringside television interview.
“We didn’t panic. We just needed time to test his power. As the fight went on, I was looking for a one-shot knockout.”
The pride of the Philippines, who had never previously fought above light-welterweight, survived an early barrage from Cotto before dominating with blistering hand speed and surprising power.
The 30-year-old dominated the official ringside statistics, connecting with 336 of 780 punches thrown to 172 of 597 for Cotto. He also landed 276 power punches compared to Cotto’s 93.
“Manny dictated the fight and they should have stopped it three rounds sooner than they did after he (Cotto) began to run,” Pacquiao’s trainer Freddie Roach said.
Cotto, who was cut above the right eye and had his nose bloodied after being repeatedly battered by Pacquiao’s jabs and punches, said: “Manny is one of the best boxers I ever fought.
“I didn’t know from where the punches were coming.”
Watched by a sell-out crowd that included basketball great Magic Johnson and Hollywood actors Mark Wahlberg and Will Ferrell, Cotto landed a couple of telling left jabs in the opening round to hold an early advantage.
Took control
Both fighters picked up the pace in the second round, exchanging thumping jabs and body punches before Pacquiao began to take control.
Pacquiao, who improved to 50-3-2 with 38 knockouts, dropped Cotto to the canvas with a searing right hook in the third round and later pinned his opponent to the ropes with a series of combinations.
Cotto struck Pacquiao with a left uppercut late in the round and landed a right uppercut in the fourth before he was again knocked to the canvas by Pacquiao’s booming left hand.
The frenetic pace continued in the fifth and sixth rounds, although the Filipino maintained overall dominance by cleverly mixing left jabs with right hooks.
In the seventh, Pacquiao landed a thudding hook and then an uppercut to leave Cotto reeling and he kept the Puerto Rican on the back foot in the eighth, twice pinning him to the ropes with a flurry of jabs.
In the ninth, Pacquiao forced Cotto to back-peddle into the corner with a furious onslaught before twice more battering his opponent against the ropes.
At that point, the fight was effectively over.
Pacquiao, who had dismantled Oscar De La Hoya and destroyed Ricky Hatton in his previous two fights at the MGM Grand, said he would not move up any higher in weight.
“It was a hard fight,” he added. “This is the last weight division for me. This is history for me and more importantly a Filipino did it.”
Cotto, who has won a world title every year since 2004, slipped to 34-2 with 27 knockouts.
