Floyd Mayweather Jr. signed off from professional boxing as he had planned, going out unbeaten and on his own terms as 'The Best Ever' after improving his career record to 49-0.

After a 19-year run that produced world titles in five weight divisions and earnings in excess of $800m, Mayweather bade farewell to the ring with a clinical display to earn a unanimous decision over fellow American Andre Berto.

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"I had a game plan from the very beginning," Mayweather, 38, said of his career during a lengthy news conference after retaining his WBC and WBA welterweight titles in the MGM Grand Garden Arena.

"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 18 years, I've had a remarkable career.

"If you put them [opponents] in front of me, we see what they can do. 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."

Mayweather, who matched the 49-0 career record set by former heavyweight champion Rocky Marciano, is widely regarded as one of the best defensive practitioners of all time while his ability to out-think opponents and adjust strategy midway through fights is unparalleled among contemporary fighters.

"I've been in the sport of boxing my whole life and they say I'm wrong for saying I'm the best."

Asked whether he might 'get that itch' to come back for another bout, as he did in late 2009 when he returned from a 21-month 'retirement', Mayweather replied: "My career is over. It's official. My 49-0 record is part of boxing".

Earlier this year, Mayweather beat Manny Pacquiao on a points decision in one of the most lucrative boxing matches of all time.

Neither of the fighters succeeded in landing a winning blow during 12 rounds and judges awarded Mayweather the fight on a points decision.

Source: Al Jazeera and agencies