The Puerto Rican superstar - already a champion in three weight classes in the last decade - added the WBC middleweight title to his lengthy career resume with a punishing 10th-round TKO of incumbent Sergio Martinez before a packed, frenzied house of 18,000 at Madison Square Garden.
It was Cotto's ninth career fight at the Garden and his eighth victory, and with it he became the first Puerto Rican to win championships in four weight classes.
He'd previously been a title-holder at 140, 147 and 154 pounds, but had lost two of his last three bouts coming into this one and had never fought at a weight heavier than 154. He joins Oscar De La Hoya as the only fighters to win championships at both 140 and 160 pounds.
"Miguel Cotto became Miguel Cotto here, and he showed that he is still Miguel Cotto here," Cotto said.
Martinez entered the ring as a heavy favorite, but he never had a chance after he was decked with a looping left hook early in the first round and wound up going to the floor three times in that round.
Cotto maintained the pressure in each and every round and consistently landed harder shots that moved Martinez every time they landed. The Argentine veteran, 39, hung in gamely through the middle rounds, but was dropped again in the ninth round when his glove touched the ground.
He'd entered the fight after missing more than a year with myriad health problems, especially with his knees, and he seemed adversely affected by his inability to elude Cotto's heavy shots. His corner waved off the fight after the ninth round, not allowing him to come off the stool for the 10th.
The official time was six seconds into the 10th round.
"He caught me cold," Martinez said. "He caught me hard at the beginning and it was hard for me to come back from that."
Cotto landed 212 of 395 punches in the fight - a staggering 54 percent - including 158 of 293 power shots, or 54 percent. Martinez landed 100 of 322 overall and 60 of 157 power shots.
SportsNetwork.com had Cotto ahead, 88-79, at the time of the stoppage.
The official scorecards had him up by 90-77 across the board, giving him all nine completed rounds.
It was his second fight with new trainer Freddie Roach, who'd trained Manny Pacquiao to a 12th-round TKO of Cotto in 2009.
"I want to rest and enjoy my family for a couple weeks," Cotto said. "Then whatever Freddie wants to do, I'll do."
On the pay-per-view undercard:
Former WBO 115-pound champion Marvin Sonsona avenged his lone career defeat with a split-decision victory over Wilfredo Vazquez Jr. in a 10-round featherweight bout.
Sonsona won two cards by scores of 96-92, while the third card favored Vazquez by the same score. SportsNetwork.com favored Vazquez, 95-93.
Vazquez had stopped Sonsona in four rounds when they met in 2010, a victory that gave the winner the vacant WBO championship at 122 pounds.
Sonsona scored well early and had the only knockdown of the fight when he dropped Vazquez with a body shot in round one. The bout was marked by frequent fouls - Sonsona was docked a point for hitting behind the head - and several periods of holding and grappling, which drew the ire of an impatient crowd in the final bout before the main event.
Sonsona landed 120 of the 463 punches he threw, while Vazquez connected on 111 of 324. Vazquez had the slim edge in jabs, 17-16, while Sonsona landed 104 power shots to Vazquez's 94.
Sonsona is 19-1-1. Vazquez is 23-4-1.
Argentine junior middleweight Javier Maciel scored the fight's lone knockdown and outhustled his foe down the stretch on the way to earning a majority 10- round decision over Puerto Rican Jorge Melendez. Maciel scored the fight's lone knockdown in the fourth round and gained another single-point advantage in that same round when Melendez was docked for low blows by referee Harvey Dock.
Maciel earned scores of 97-91 and 96-92 on two scorecards, while the third was even, 94-94. SportsNetwork.com had Maciel up, 95-93, after giving him rounds three, four, seven, nine and 10.
Maciel landed 177 of 481 punches, or 37 percent, while Melendez connected on 149 of 603, for 25 percent. Maciel had a 156-111 in power shots. Melendez led, 38-21, in jabs.
Maciel is 29-3. Melendez is 28-4-1.
Irishman Andy Lee pulled victory from the jaws of what was veering toward unimpressive defeat when he dropped John Jackson with a single right hand at 1:07 in the fifth round to win their scheduled 10-round junior middleweight bout.
Jackson had knocked Lee down with a right in the first and landed the better shots through four rounds, then wobbled him again in the fifth before Lee ripped a blistering counter hook that sent Jackson face-first to the floor. Referee Ricky Gonzalez waved the fight off before completing the count, lifting Lee to 33-2 with his 23rd knockout. Jackson is 18-2.
SportsNetwork.com and all three official scorecards had Jackson ahead, 39-36, at the time of the stoppage.
On the non-televised undercard:
Former Olympian Felix Verdejo improved to 13-0 and scored his fourth early win in New York City, stopping Engelberto Valenzeula after just 77 seconds of their scheduled six-round lightweight bout. Verdejo, who represented Puerto Rico in the 2012 Summer Games, has first-round wins in each of his four New York appearances - two at the MSG Theater, one at Radio City Music Hall and now one in the Garden's main room. Valenzeula is 8-2, with both losses by first-round stoppages.
Twenty-year-old prospect Jose Lopez ran his record to 14-0 with a unanimous eight-round decision over Raul Hidalgo in a 122-pound bout. Lopez had 11 KOs, including five in a row heading into the bout, but never seriously hurt his man in a chess match that drew boos from the gathering crowd. He won by wide scores of 80-72, 80-72 and 79-73. Hidalgo is 21-11 with one no-contest.
Unbeaten Jose Pedraza, who holds the IBO's world title at 130 pounds, moved up to 135 and improved his record to 17-0 with a first-round stoppage of Arturo Uruzquieta in a scheduled six-round match. Uruzquieta was dropped into a corner after a flurry of blows, which prompted the intervention of referee Arthur Mercante Jr. Uruzquieta is 15-6.
Ohio-based middleweight Willie Nelson won his sixth straight bout and improved to 22-1-1 as a pro with a first-round TKO of Darryl Cunningham in a scheduled six-rounder. Nelson dropped Cunningham twice and had the win sealed for him when the referee - at the urging of the ringside physician - waved the fight off at 2:43. Cunningham is 29-7.
Former Puerto Rican Olympian Jantony Ortiz was a smashing success in his pro debut, dropping flyweight foe Elio Ruiz with a flurry in his corner and then watching him take the 10-count at 1:50 of round one of a scheduled four. Ruiz is 1-5.