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."
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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.
The pattern for the fight, as with so many of Mayweather's previous fights, was set in the opening round, the champion establishing his lightning jab and repeatedly making Berto miss.
|Mayweather-Marciano head to head|
|Floyd Mayweather||Rocky Marciano|
|Money||Nickname||The Brockton Blockbuster|
|Las Vegas, Nevada||Home town||Brockton, Massachusetts|
|24 February 1977||Date of birth||1 September 1923|
|Super-feather to light-middle||Weight||Heavy|
|49 wins (26 KOs), no defeats||Pro record||49 wins (43 KOs), no defeats|
|26||World title fights||7|
Mayweather went on the back foot in the second but Berto was chasing shadows, before the champion came out punching in the third, catching his rival cold with a snapping left hook.
After the first nine minutes of action Berto had barely laid a glove on Mayweather, and Mayweather made the challenger's knees sag with a flashing overhand right with a minute left in the fourth.
Berto continued to venture forward in the fifth but even when he managed to manoeuvre Mayweather onto the ropes, he was unable to land with any meaningful blows.
Berto might have done enough to win the sixth and certainly won the seventh, during which he landed with a clubbing left hook.
Mayweather was happy to coast through the eighth, winning it on the back foot while drawing boos from the crowd as he mugged on the ropes.
A fight broke out towards the end of the ninth, with both men trading blows on the bell, and the rivals were broken apart and warned for trading words in the 10th.
Mayweather looked like he might open up in the 11th, landing with a cute uppercut, but he was showboating again towards the end of the round.
And the fact there were boos ringing around the arena as the final round was drawing to a close rather summed up Mayweather's career - to many he is a genius, but he leaves many more boxing fans cold.
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.
'I'm not perfect but I strived to be a perfectionist'
Speaking in a 45-minute post-fight news conference, Mayweather said: "I had a game plan from the very beginning. I always knew what I wanted to do - be outspoken, be one of a kind. To be in the sport for 19 years and to be world champion for 18 years, I've had a remarkable career.
"It's all about that IQ. I'm 10 steps ahead of any fighter, I take whatever is your best attribute and take that away from you, make you do what you don't want to do.
"Every champion - Muhammad Ali, Sugar Ray Robinson, Sugar Ray Leonard, Larry Holmes, the list goes on and on - they opened up the doors and paved the way for where I am today and I'm appreciative.
"But now the young fighters say, 'We want to be like Mayweather'. It's not cool to take punishment in the ring. I'm not perfect but I strived to be a perfectionist."