LAS VEGAS -- Few question the credentials of lightweight champion Juan Manuel Marquez. His accomplishments speak for themselves.
He's widely considered Mexico's No. 1 active boxer and ranks No. 2 on most pound-for-pound lists. He has won world titles at featherweight, junior lightweight and lightweight while beating a number of quality opponents.
In his only two fights at lightweight, he scored crushing knockouts against respected foes, stopping Joel Casamayor in the 11th round in September 2008 to claim the lineal title and blasting out Juan Diaz in the ninth round in February in a fight of the year candidate.
Marquez also owns convincing victories against Marco Antonio Barrera and Rocky Juarez and was in a pair of pitched battles with pound-for-pound king Manny Pacquiao, getting the short end of a one-point split decision in a 2008 junior lightweight championship fight and being held to a draw in a 2004 featherweight title bout.
There are legions who believe Marquez won both fights with Pacquiao. "We all know Marquez beat Pacquiao," said Marquez promoter Oscar De La Hoya.
However, despite all he has accomplished, combined with an essentially even-up display through 24 grueling rounds against Pacquiao, few give Marquez much of a shot against unretiring former pound-for-pound king and five-division champion Floyd Mayweather Jr. when they meet in a 144-pound fight at the MGM Grand Garden Arena on Saturday night (9 ET, HBO PPV, $49.95).
Marquez (50-4-1, 37 KOs), who is moving up two weight divisions, is a heavy underdog. According to the MGM sports book, Mayweather (39-0, 25 KOs) is a 4-1 favorite, which is huge by boxing odds standards.
No matter, said Golden Boy CEO Richard Schaefer.
"He's a man on a mission," he said of Marquez at Wednesday's final news conference.
Marquez doesn't seem offended that he's such a significant 'dog.
"I think that life is full of surprises," Marquez said through an interpreter. "This is what motivates me. This is what makes me train hard. When I wake up in the morning, it makes me want to train harder, run faster and longer. These are the kind of fights that motivate me. I'm going to prove everybody wrong."
But seeing Marquez pose for photos with Mayweather after the news conference illustrated that he is clearly the smaller man. Mayweather is also a very fast fighter with superb defense.
Marquez and his team know the fight is an uphill battle, but they sound confident.
"We have worked so hard for this fight that we have the illusion and belief we can win," said Nacho Beristain, Marquez's longtime trainer and one of the most revered cornermen in Mexican boxing history, through an interpreter.
Said 36-year-old Marquez: "By far, I feel he's the best. He's undefeated. He retired, and he's still considered to be the best pound-for-pound in my eyes and in a lot of people's eyes. It's a very hard fight, but mentally I'm preparing myself to win and I feel I can beat Mayweather."
Marquez, too, tips his hat to Mayweather's record and reputation when asked whether he believes this will be his toughest fight.
"Yes, definitely, I do believe so," said Marquez, who estimated he's been training for about five months for the fight because it originally was scheduled for July 18 but was postponed when Mayweather suffered a rib injury. "He's a counterpuncher, he's very fast and elusive and also a very defensive fighter, so that will make it much more difficult.
"It's going to be a very difficult fight. I am going to come in with a lot of speed, like I have always done, and that makes it very difficult. You've got to come in and bob and weave and bend and make him miss, and then counter him and wait for the right moments and pick your shots."
Mayweather has tried his best to downplay his size advantage, but facts are facts. Mayweather hasn't fought at lightweight since 2003. He beat De La Hoya at 154. Marquez is a career featherweight (126 pounds) with only his past five fights coming at junior lightweight (130) or lightweight (135).
"They said Sugar Ray Leonard had [all the advantages], but Roberto Duran came from lightweight to welterweight to beat Sugar Ray Leonard, so we could never say never," Mayweather said.
What Mayweather failed to mention was that by the time Duran beat Leonard in their first meeting, he had fought his eight previous fights at welterweight.
Although Mayweather almost certainly will be the faster fighter, De La Hoya explained that a fighter with a good jab, which Marquez has, often can neutralize speed.
The jab is one of the reasons De La Hoya cites as to why he thinks Marquez will pull the upset.
"When I fought Floyd, my jab was the key," De La Hoya said. "You know I have a great jab, and when I used it, I was unstoppable. That was my key to victory. When I stopped using it, that's when Floyd was able to win the fight. Marquez has an excellent jab. Marquez is going to use the triple, the quadruple jabs.
"This is the fight of his life. This is the opportunity of a lifetime, and he knows it. He's a smart counterpuncher. He's a smart fighter, and it's a matter of throwing those jabs and feigning those jabs, and not only throwing the jab but putting three, four, five punches right behind that jab. That's going to be the key."
Whatever happens, nobody is going to say Marquez didn't go to great lengths to prepare himself.
There was the usual intense running (including at altitude in the mountains outside of Mexico City) and sparring. But Marquez also has employed some unusual training techniques in the belief they will help him come Saturday night.
Marquez ate raw quail eggs, and he and spent time in a hyperbaric chamber to replenish his oxygen levels. Then there was the drink seen 'round the world, courtesy of HBO's "24/7" series, which has been following both fighters in the buildup to the fight.
Marquez regularly drank his own urine, believing it helps replenish nutrients in his body, even though most experts call it an old wives' tale and say that although ingesting urine won't hurt, it is not of any help, either.
Still, Marquez has to be a tough man to drink his own pee, which he actually seemed to enjoy in HBO's footage.
"I think that this has helped me," Marquez said on "24/7." "I've done it for the last five or six fights with good results. I also drink my urine because that's where a lot of proteins and vitamins are, part of your vitamin intake, and why not drink them again instead of wasting them?"
If Marquez -- who figures to have the crowd on his side because the fight is on the weekend of Mexican Independence Day, a traditional weekend for a big fight -- has a single advantage, it might be that Mayweather is coming off a long layoff.
Although Mayweather retired, few expected him to remain out of the ring for long. Still, it will be nearly two years since his last fight. Marquez, however, is downplaying the possibility of catching a rusty Mayweather.
"That's not even in my mind," he said. "We're not working or training for Mayweather that's been out of the ring or that can be less fast. I'm training for the best Mayweather there is. And that's what we're working hard to achieve, working on the speed, working on the strategy inside the ring. We're looking forward to facing the best Mayweather."
Mayweather has paid similar compliments to Marquez rather than verbally attacking him the way he has done to so many past opponents.
"Marquez is a Mexican warrior. He represents the Mexican community extremely well and the heritage extremely well," Mayweather said. "I know he's going to be at his best when he comes to face the best, so the only thing I've got to do is go out there and be me. Be sharp and be smart.
"Marquez is a hell of a fighter, counterpuncher, good boxer. But I've been around the sport and I have faced many different styles. So, I'll adjust and adapt when I get in that squared circle Saturday night."
Whether De La Hoya truly believes Marquez will win or it is just promotional bluster, he's doing his best to make convincing arguments on Marquez's behalf.
A Marquez win would be a major upset, even though Mayweather hasn't fought since knocking out Ricky Hatton in December.
"I just have this feeling that Marquez is going to pull this one off," said De La Hoya, who lost to Mayweather in 2007 and has no particular love for him. "I went down to Mexico and saw him train with my own eyes. I saw how much he bulked up. I saw how much strength he has gained. I saw how seriously he's taking this fight, and I'm convinced he will win this fight. He's looking sharp, he's looking fast, he's looking strong.
"Floyd Mayweather is the best fighter on the planet, and Juan knows that. He knows he's up for a big challenge, but he's ready and he knows that he has to put his life on the line and he's willing to do that. So it's going to be one tremendous fighter against another tremendous fighter. And so I just have this feeling, after watching Marquez, he's going to pull it off."
Dan Rafael is the boxing writer for ESPN.com.