Mayweather (45-0, 26 knockouts) made the decision known on his verified Twitter account that he would fight Maidana (35-3, 31 KOs), whose manager, Sebastian Contursi, said the fighter was oblivious to the announcement until being informed by him nearly an hour later.
"Marcos knew that he had a really good chance of being chosen, but I wanted the news to surprise him. So I just talked to him about 20 minutes ago, and that's when he found out," said Contursi, during an interview with RingTV.com from Buenos Aires, Argentina, on Monday evening.
"Marcos is a very special guy with a very special personality, so he didn't pay much attention to the stuff on the internet. He's from a small town in the country in Argentina. So at the moment that Floyd made his announcement, he was not aware of it. So he learned from me that Floyd Mayweather had picked him."
On his Twitter, Mayweather wrote "I will be fighting Marcos Maidana May 3rd on Pay-per-view Showtime/CBS," ending months of speculation that included feedback from fans across an array of social media platforms concerning who will challenge for his RING and WBC 147-pound championships.
"Marcos Maidana’s last performance immediately brought him to my attention," Mayweather said, referring to Maidana's upset victory over Adrien Broner in December.
"He is an extremely skilled fighter who brings knockout danger to the ring. I think this is a great fight for me and he deserves the opportunity to see if he can do what 45 others have tried to do before him — beat me."
Mayweather's decision verified what Khan (28-3, 19 KOs) already knew on Friday, when the frustrated former 140-pound beltholder tweeted his knowledge of Mayweather's choice despite having stated publicly in December that he already had signed his contract to face Mayweather.
Still, Contursi contends that he was unsure that Maidana was the man who would be in the ring against Mayweather until midnight on Sunday, when he received a phone call from Golden Boy publicist, Marylyn Aceves.
"I probably knew for sure last night, when I received a call at about midnight yesterday. It was a call from Golden Boy's publicist, Marylyn Aceves about Marcos," said Contursi of Maidana, 30, who will bypass a previously considered rematch with Broner to engage in the biggest fight of his career.
"She wanted us to review certain quotes that Marcos was going to say if he was the chosen one. But you recall that two months ago, Amir Khan said that had a contract that he had signed. He told the British press that he was sure that he was going to be the chosen one."
As late as last month, Contursi contended that Mayweather's mention of Maidana over Khan was "a smoke screen."
"I never could be sure, so I never wanted to generate any false expectation, because, you know when it involves Mayweather, it's a complicated situation," said Contursi. "There a lot of things that you have to take care of and there are many different points. But when I received that call from Marylyn, then I was sure that it was going to be Maidana. But it was too late, so, to be honest, I didn't call him."
Maidana is 4-0, with three knockouts as a welterweight since falling by unanimous decision to Devon Alexander in his 147-pound debut in February 2012. That run includes stoppage victories in the sixth and eighth rounds over Josesito Lopez and Jesus Soto Karass.
"I am extremely happy to be facing Floyd Mayweather because it will give me the opportunity to show the world that I am the best welterweight in the division," said Maidana, in a statement.
"I just handed a great defensive fighter his first loss, and I plan to do the same to Mayweather. I don't care whether he's the best and undefeated. I will bring some real Latino power to him on May 3."
Possible venues have been narrowed down to the MGM Grand in Las Vegas and Barclays Center in Brooklyn, N.Y., and Golden Boy CEO Richard Schaefer said he will soon decide which will receive Mayweather-Maidana.
"That's something which I'm working on, and that I'm hoping to finalize within the next 24-to-48 hours," said Schaefer. who added ticket information was forthcoming.
Maidana represents the third fight in a lucrative 30-month, six-fight deal signed by Mayweather with Showtime and its parent company CBS that could be worth a guaranteed $250 million, according to an online report by Forbes Magazine.
"In Marcos Maidana, Floyd Mayweather may be in for his toughest opponent ever. Maidana is the type of fighter who will find out if Floyd still belongs on top of the pound-for-pound list. He's strong, tough and aggressive," said Schaefer.
"In giving Adrien Broner his first loss, he showed that he won't be intimidated by talk, a big fight atmosphere or an unbeaten record. I give Floyd a lot of credit for stepping up to the plate and testing himself once again. He is a true warrior, and the fans will be the winners on May 3."
Mayweather was last in the ring in September, when he dethroned Canelo Alvarez for the RING and WBC 154-pound championships by majority decision in a fight that grossed $150 million.
In May 2013, Mayweather unanimously decisioned Robert Guerrero in defense of the WBC 147-pound title he had earned by dethroning Victor Ortiz via fourth-round stoppage in September of 2011.
"The first two events in our partnership with Floyd Mayweather were incredible, and Showtime Pay Per View is proud to present the next chapter in Floyd's remarkable career," said Stephen Espinoza, executive vice president and general manager, Showtime Sports.
"Marcos Maidana is a boxer whose fearsome power can change the trajectory of a fight with a single punch. Couple that with his ferocity and perseverance and you have the recipe for an incredible fight on the grandest stage of the sport."
The win over Guerrero cemented Mayweather's status as RING welterweight champion as well a year after Mayweather's unanimous decision over Miguel Cotto won the WBA's 154-pound belt in May 2012.
"This is an extremely dangerous fight for Floyd as Marcos Maidana is a technical knockout artist and continues to show us that he gets better with each fight," said Leonard Ellerbe, CEO of Mayweather Promotions. "Maidana showed so much in his last performance, he's clearly at the top of his game and a great match-up for Floyd."