Singer-actor Ruben Blades was a member of the Roberto Durán entourage when his fellow Panamanian was at the top of the boxing world. But he happened to be in New York for the infamous “No más” fight, and had to watch it on closed-circuit (the Pay-Per-View of its day).

“There was this girl I always wanted to go out with,” Blades remembered. “I asked her many times and she always said no. Finally, she said yes and I told her, ‘Well, we’re going to go have dinner and dance, but first we have to go see the fight.’ So we went to see it at the Beacon Theatre. And when that happened I said to the girl, ‘Have a good night.’ I put her in a cab. And I never saw her again.”

“That” was Durán’s surrender in the eighth round of his Nov. 25, 1980, welterweight championship bout with Sugar Ray Leonard, reportedly muttering “no más” (“no more”) to the referee and walking away — a cataclysmic moment in boxing history and the climax to “Hands of Stone,” Venezuelan director Jonathan Jakubowicz’s bio of the celebrated prizefighter (opening Aug. 26). It was an act that rattled fight fans around the world, to say nothing of the people close to Durán.

“I went to sleep crying,” said Blades. “Freddie Brown [one of Duran’s trainers] called me at 7 a.m. to ask me if I knew what happened. Which tells you something.”

In the film, as in life, Durán — played by the director’s fellow Venezuelan, Edgar Ramírez (“Carlos,” “Joy”) — grows up in gritty Panama City, poor and fatherless; he steals mangoes from the hated U.S. Canal Zone to feed his crowd of siblings and first gets into the ring at the age of 8, having battled on the streets for years.

His acquires a pair of father figures on his way to the lightweight championship: his manager, the wealthy Carlos Eleta (Blades), who bankrolls his career, and his trainer, the celebrated Ray Arcel — given a portrayal by Robert De Niro that will no doubt be generating conversation around awards time. It is Eleta who pushes Duran into a second fight with Leonard, wanting to cash in on the obvious excitement surrounding a rematch. (Durán had beaten the popular Leonard in Montreal six months earlier.) Arcel opposes the fight, as does Durán, who famously liked to live it up — and eat — between bouts. The movie maintains, just as it subject always has, that stomach cramps due to rapid weight loss led to him turning his back on his opponent, and committing the unheard-of crime of quitting a professional prizefight.

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In “Hands of Stone,” the glories are counterbalanced by the shame that followed the “no más fight.” As Ramírez noted in a recent interview, Panama is a country with only 30 million people, and it has had 29 world boxing champions. “Boxing here is like football in Brazil,” he said. “It’s part of everyday life. Roberto Durán brought so much glory to this country. He’s more than a national hero — he’s like the soul of Panama. Everyone has a story with Roberto. Everyone has an anecdote with him at a bar or a park or a restaurant. He embodies the soul of the country. It’s really amazing.” And when he quit the Leonard fight, the reaction among his countrymen was predictable.

But Ramírez’s experience seems to have been strictly positive. “The first time I shot in El Chorrillo,” he said, referring to the impoverished area where both Durán and former President Manuel Noriega came from, “I was pretty nervous. I was supposed to be the young Durán, 19 or 20 years old. I got to the set and suddenly this old guy turns around and shouts, ‘Oh, my God, that’s Durán!’ He was looking at me, and he said, ‘That’s Durán at 146 pounds!’ . . . and I almost cried.”

Blades hasn’t seen the film, he said, but he admired the story because it understands how multilayered real life can be.

“There’s a tendency to demonize people in general, and I know from experience things are more complicated than what they seem,” said the actor, who has a recurring role now in “Fear the Walking Dead.” The relationship between Eleta and Duran was like a father and son, and there was some competition between Arcel and Eleta for Durán’s affection.

“As greedy as Eleta may seem to some,” Blades said, “he forced Durán to put money in a CD. It is a known fact Roberto never wanted to fight for a while after a match; he wanted to eat and carry on.

“So Eleta’s position wasn’t just, ‘He’s becoming more and more irresponsible, and if I don’t make money off him now, I never will,’ ” Blades said. “But also, ‘If he doesn’t make money now, he never will.’ ”