Floyd Mayweather makes his first appearance of 2014 at the MGM Grand in Las Vegas on Saturday against the rugged and hard-hitting Marcos Maidana, who despite a solid pedigree is a prohibitive underdog. Mayweather is fond of saying 45 opponents have tried and 45 have failed to defeat him.

But Jose Luis Castillo and a legion of fans and observers disagree.

On the night of April 20, 2002, at the MGM Grand, long before Mayweather became a transcendent figure and boxing's biggest draw, he was a young, up-and-coming prizefighter building his career. After a productive run as a junior lightweight (130-pounds), Mayweather moved up to face Castillo, who held the WBC lightweight (135-pounds) belt. Mayweather, then "Pretty Boy," was a sizable favorite and many thought Castillo was merely keeping the belt warm for him.

"I knew that he was an Olympian and that he was very talented," recalled Castillo, speaking from Mexico, with his current promoter, Luis DeCubas, translating.

Mayweather was just 25 years old and had a professional mark of 27-0. This bout was thought to be an easy one for the prodigy out of Grand Rapids, Mich. Castillo, was a tough, hard-nosed plugger -- known for cutting his teeth as Julio Cesar Chavez's sparring partner -- and the type of guy Mayweather could easily out-box.

A funny thing happened on the way to this coronation. Castillo didn't go by the script. After a slow start and trouble dealing with Mayweather's skill, Castillo adapted and was able to crowd and pressure the slicker Mayweather, forcing him to back up for much of the night. It was clear Mayweather -- making his first start as a legitimate lightweight -- had problems with the size and strength of Castillo, but also that the craftiness of the Mexican was underrated.

"I think, to a certain degree, he underestimated me, but he was certainly very good, very difficult to catch," Castillo said. "He also had very good speed and quickness but I just kept putting pressure on him as much as I could."

It was a tale of two fights, the first half controlled by the boxing of Mayweather, the second dictated by the intelligent relentlessness of Castillo. This wasn't just about the brawn of Castillo, but also his boxing I.Q. As the final bell sounded, Castillo believed he had retained his title.

"Oh, no doubt, after 12 rounds I thought I had done more than enough, certainly more than he did," a rueful Castillo said. "But they didn't give me the decision."

Judge Anek Hongtongkam had Mayweather up by the score of 116-111 and John Keane and Jerry Roth scored it 115-111 for the challenger.

In many ways you could call it a business decision, after all, while both were then under the Top Rank promotional banner, it was Mayweather who was the American and former Olympian, who had the HBO contract and the upside. Mention this to Castillo, he says with a sigh, "Well, I don't want to say the wrong thing, but boxing is certainly filled with interests, let's put it that way."

Social media platforms teem with heated debates over the fight. There is a sizable contingent who believes Mayweather record should stand at 44-1. Harold Lederman scored the fight 115-111 for the Mexican.

"I thought Castillo beat him, period, end of story," Lederman said, with his trademark laugh. "I thought he out-punched him. I thought he landed more clean, telling shots. I thought he just beat him."

Larry Merchant, who was ringside calling the fight for HBO said, "I think that Mayweather fought the wrong fight. He tried to stand and fight him and so it became a close fight." As for who he had winning, Merchant added, "I remember saying I thought Castillo won."

(For the record, I was on press row and had Castillo 116-112. Doug Fischer of RingTV.com had Mayweather up 115-114, while Kevin Iole of Yahoo Sports had it 115-113 in favor of Mayweather)

There was enough debate and controversy that eight months later they met again in Las Vegas. Mayweather, utilizing much more movement, skated to a convincing victory.

"If you look at the scorecards, the fight was actually very close, but after 10 rounds I got discouraged in just chasing him around the ring and I kinda gave up, to be honest," Castillo said. "I didn't realize the fight was actually that close with the judges."

Ironically, the second fight was much closer on the cards. Judges Ken Morita and Daniel Van de Wiele each had it 115-113 for Mayweather and Larry O'Connell scored it 116-113. While Mayweather has gone on to greatness, Castillo will always have a place in history for being the man who gave him his sternest test. That in itself, is quite an achievement.

"Even though I lost and didn't get that decision, it is still something I'm very proud of," Castillo said. "Not a lot of fighters that have faced him have gotten nearly as close as I have."

Castillo, however, shouldn't be remembered solely for troubling a great fighter. The fact is, Castillo has had an incredibly distinguished career -- still on-going as he plays out the string past his prime like many other boxers. He was able to regain his WBC title after Mayweather moved up and vacated it. His résumé includes quality victories over Stevie Johnston, Cesar Bazan, Juan Lazcano, Joel Casamayor and Julio Diaz.

Then, there was his first matchup against Diego Corrales in 2005, which just might be -- and this is no exaggeration -- the greatest fight of the 21st century. It's the most awe-inspiring fight I have covered live. Boxing News published the "100 Greatest Fights of All-Time" a few years ago and ranked Corrales-Castillo I seventh. In defeat, Castillo covered himself in glory. Before he became a pugilistic pariah for his inability to make weight, as his body finally had enough of shrinking itself down to 135 pounds, this guy was one helluva fighter.

"Castillo's been in a lot of great fights, without a doubt, and everyone thinks Mayweather's the best fighter of the past 20, 25 years, so you can always look at that fight," DeCubas said. "And of course you're going to look at the Corrales fight, the Casamayor fight. They're going to talk about a lot of those fights. I've been in boxing for 32 years and this guy's one of the nicest guys I've ever met. He's a class act, I gotta tell you."

There is no particular bitterness with Castillo, who has always been among the most amiable individuals in the sport. But he wonders how different things would have been if the scores read in his favor versus Mayweather. For much of his prime, he was overshadowed by his Mexican counterparts, Erik Morales, Marco Antonio Barrera and Juan Manuel Marquez. A victory over Mayweather could have gone a long ways in cementing his status as an all-time great Mexican fighter.

"I think about it a lot," Castillo said. "It would have not only changed my career but probably my life. Just the type of money I would have made."

As for any advice he'd give to Maidana, Castillo said, "He's going to have to pressure, back him up and do what he did against Adrien Broner. Go go the body and stay there as much as he can."

Castillo, now 40, makes a strong case for induction into the International Boxing Hall of Fame. Mayweather, long ago put in his reservation to Canastota, but for one night, a dozen years ago, Mayweather looked human thanks to this unassuming man from Sonora.

Is Castillo surprised by the heights reached by his former rival?

"No, because I know how good he was and could be," Castillo said, before adding, "I didn't fight in the era of Rocky Marciano, Muhammad Ali, or anything like that, but he's certainly the best boxer that I faced."

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Steve Kim began covering boxing in 1996 and has been writing for Maxboxing.com since 2001. He is also a regular contributor for Boxing News. He can be reached at k9kim@yahoo.com and he tweets (a lot.)