As Floyd Mayweather Jr. likes to say, 42 have tried and 42 have failed to take his undefeated record.

But along the way, Mayweather has encountered at least a few problems. Jose Luis Castillo gave him a very tough time in two lightweight championship fights in 2002, both of which Mayweather won by decision. Many believe Castillo outright won the first fight. (I had it a draw.)

Former titlist DeMarcus "Chop Chop" Corley rocked Mayweather in his 2004 junior welterweight debut. In a 2006 welterweight title fight, Mayweather had difficulty with Zab Judah in the early rounds, even touching his glove to the canvas for what should have been a legitimate knockdown, though referee Richard Steele missed it.

Oscar De La Hoya gave Mayweather a tough fight for six rounds in their 2007 junior middleweight championship fight before he abandoned his jab and faded. Mayweather won a split decision.

And Shane Mosley had one huge moment in the second round of their 2010 welterweight title fight. He badly rocked Mayweather but was unable to finish him. Floyd recovered and won the rest of the fight going away in a lopsided decision.

Now, as Mayweather prepares to challenge junior middleweight titlist Miguel Cotto on Saturday in Las Vegas, he has been repeatedly asked to rate Cotto among his opponents. The funny thing: None of the fighters mentioned above gave him the most trouble. That distinction belongs to journeyman Emanuel Augustus, who became a fan favorite because of a series of entertaining fights on ESPN2. (Remember his 2001 fight of the year against Micky Ward?)

"I think that I can't really just put a certain number on Miguel Cotto, because at this particular time if I was rating certain fighters out of every guy that I fought, I'm going to rate Emanuel Augustus first compared to all the guys that I've faced," Mayweather said on a recent conference call with boxing reporters. "He didn't have the best record in the sport of boxing, he has never won a world title, but he came to fight and, of course, at that particular time I had took a long layoff."

In October 2000, Mayweather, junior lightweight champion at the time, was coming off a seven-month layoff -- the longest of his career at that time -- because he was in a snit with HBO over the terms of his multi-fight, multi-million dollar contract, which he had referred to as "slave wages."

But they finally worked things out, and Mayweather's return in a nontitle bout at lightweight was set to help the struggling (and now-defunct) Saturday afternoon series "KO Nation."

Augustus -- known then as Emanuel Burton -- got the assignment. Even though Augustus' record was 22-16-4 going into the bout, it was quite misleading because he could really fight.

I covered the fight for USA Today at Cobo Hall in Detroit, and Augustus gave Mayweather hell before his corner stopped the fight in the ninth round, with Augustus bleeding and in trouble. Until the stoppage, most of us at ringside were very surprised by what we were seeing.

"You need to realize, I was the guy that was fighting every two to three months," Mayweather said, "and then I took almost a year off and I fought a guy that fought normally at 135, 140, and I moved up from 130. So that's why I think that was probably a little difficult -- but not really, because like I said before, I could solve any problem."

Three months later, Mayweather returned to 130 pounds and defended his title in a tour de force against the late Diego "Chico" Corrales. Mayweather dropped him five times en route to a 10th-round TKO and handed him his first career defeat in a performance much sharper than on that day in Detroit.

Augustus continued to fight regularly over the next decade, losing more often than he won. He fought as recently as January 2011 (when he was robbed against Vernon Paris) but has lost five in a row. Still, nobody can ever take away his near upset of one of the best fighters of all time.

"Whosever on the line [that] really don't know the career of Floyd Mayweather, look him up," Mayweather said of Augustus. "He's a tough opponent. What else could I say?"