Cotto, 37, had announced before the defence of his WBO light-middleweight title that the fight would be his last. Sadam Ali stood in against him, but the 29-year-old Brooklyn fighter and former U.S. Olympian didn't come to be Cotto's last victim.
Round 6 saw Cotto deliver a right hook that sent Ali flying to the ropes, reminding the younger fighter whose goodbye party it was. But Ali really came on strong in the second half of the fight, after Cotto said he hurt his left biceps in the seventh round.
After 12 rounds the judges scored the fight 115-113, 115-113, and 116-112 to Ali.
"I am feeling good with the performance", the always classy Cotto, as dignified in disappointment as he always had been gracious in victory, said in reaffirming his intention to enter retirement and enjoy the remainder of his life with his handsome wife Melissa and the couple's two children.
"I just wanna say that when we were entering into this fight", Rozier said, "all the naysayers who thought that Sadam couldn't win will probably be the same guys who said that Sadam won by whatever". I am proud to call Madison Square Garden my second home.
"Thank you for supporting me at every opportunity", Cotto told his fans. "They could have taken an easier fight".
Miguel Cotto v Sadam Ali: Surprise points defeat for WBO champion in final bout
"I dare to be great, like Oscar De La Hoya says".
Ali added: "Good things happen to good people".
But Ali looked strong, fast and determined against Cotto, as he dropped Cotto to 8-2 at the Garden and 20-6 in world title fights, many of them among the most memorable in recent boxing history. Ali then turned the tables on Cotto in the 4th, landing overhand right hooks that stopped Cotto in his tracks and building his confidence.
The Garden had a familiar ring for Cotto. I have been training since I was eight years old, and I am glad I got this win at MSG, in my hometown. Sadam won the fight. So he improved to 31-0, while Negrete fell to 17-1.
The 27-year-old from Puerto Rico was back fighting for the first time since his first loss. Frugal with his money and mindful of his health and well-being, he steps away far better off than many champions who only considered the present and were never mindful of the potential pitfalls of the future were they to linger too long in an unforgiving game. He fought gamely, trying his best to apply pressure and bore his way in with compact power shots, and did make this a competitive farewell encounter, even rocking Ali with a straight right in the 6th. Had he dominated Ali, one could imagine him perhaps getting the itch to take on a Canelo Alvarez or Gennady Golovkin, which was the initial plan.
Acosta had Alejo, 33, of Mexico, in trouble throughout the later rounds.