Floyd Mayweather made it 49 straight wins with a wide points victory over Andre Berto in Las Vegas.
The challenger was game but his fellow American, defending his WBC and WBA welterweight titles, was simply too difficult to hit at the MGM Grand.
Mayweather, 38, was awarded the verdict 120-108, 118-110 and 117-111.
Mayweather was adamant it was his last fight, but having equalled Rocky Marciano’s career record of 49-0, he might decide to have one more.
“My career is over, that’s official,” said five-weight world champion Mayweather, widely regarded as the greatest fighter of his generation.
“You’ve got to know when to hang them up. I’m close to 40 now. There’s nothing left to prove in the sport of boxing. Now I just want to spend time with my family.
“I am leaving the sport with all my faculties, I’m still sharp and smart.
I’ve accomplished everything in this sport, there’s nothing else to accomplish.”
The 32-year-old Berto is a two-time welterweight world champion and came into the fight having lost only three of his 33 professional bouts.
But those three defeats came in his previous six contests and pretty much nobody gave him a chance against Mayweather, who was engaging in his 26th world title fight and whose unbeaten streak goes back to 1996.
Mayweather made $34m (£22m) for his latest outing but few expect him to fulfil his promise to retire.
MGM’s new arena opens next April and a rematch against Manny Pacquiao, whom Mayweather beat in May in the richest fight in history, or against the winner of Miguel Cotto-Saul Alvarez might prove too tempting to turn down.