Juan Manuel Marquez (left) and Juan Diaz get a good look at one another after the final news conference for their rematch Saturday in Las Vegas. Photo / Gene Blevins-Hoganphotos-Golden Boy Promotions

LAS VEGAS – Some observers and fans believe the recent past suggests that Juan Diaz is in decline at 26.

Diaz started his career 30-0 but is only 2-3 since, his losses coming against Nate Campbell, Juan Manuel Marquez and Paulie Malignaggi. In his last two fights, a disputed victory and a clear setback against Malignaggi, he looked mediocre.

That perception is fine with Diaz and his trainer, Ronnie Shields. It’s also an illusion, they say.

They both said that anyone who judges Diaz based on the Malignaggi fights could be surprised when the Houstonian faces Marquez in a rematch of their 2009 Fight of Year on Saturday at Mandalay Bay.

Diaz said it was a mistake to move up to 140 pounds to fight Malignaggi because he felt undersized at that weight, which is why he’s back down to a more-natural 135 pounds for Marquez.

“I give a lot of credit to Malignaggi,” Diaz said as he was surrounded by a small group of reporters at the final news conference on Wednesday. “He’s an awkward fighter. On top of that, it was another weight class. I know now I made a mistake fighting a second fight. I should’ve just got my win in the first fight and said, ‘You know what? I’m going back to lightweight. If you want to fight me, come down to lightweight. If not, there’s no rematch.’

“That was my mistake. Now I know 140 pounds isn’t for me. Lightweight is my class.”

Shields shook his head at the perception of his fighter.

“They don’t know Juan Diaz,” he said. “You can’t judge him on going up to 140 pounds and fighting Paulie Malignaggi. He has a different style, a guy who runs all over the place. People who judge him on that don’t know boxing. Wait until Saturday night and then make an assessment. To make an assessment before the fight is crazy.

“I’ve been getting a lot of calls from people who think Floyd (Mayweather Jr.) took a lot out of Marquez. Let’s just wait and see.”

The prevailing thought also is that Marquez might’ve taken something out of Diaz in the first fight, a thrilling (and taxing) brawl that ended with Diaz flat on his back in the ninth round.

Diaz said he recovered quickly after the fight and isn’t fazed by either the result or the way the first fight ended. He insisted he isn’t at some kind of psychological disadvantage because he was stopped.

“I’m smart enough to know that in boxing you can get knocked out or cut,” he said. “If you’re not up for the challenge, if you’re scared of all those things, then don’t do it. If I were afraid to come in Saturday night and get knocked out or cut, I wouldn’t do it.”

Pressure got to him?: Normally, fighting in front of hometown fans is an advantage for a fighter. That might not have been the case when Diaz met Marquez in Houston, according to Shields.

“I think the pressure of fighting in Houston had a lot to do with the result,” he said. “That fight meant so much to him. He just wanted to win so bad in front of everybody that the pressure got to him. He wanted to annihilate the guy.

“There’s no pressure here at all. I wish the first fight was here.”

Diaz also said that he sometimes gets caught up in emotion, which he worked to control in training camp.

“I worked really hard in the gym to not let that happen in this fight,” he said. “I controlled my emotions. My sparring partners hit me with good, clean shots and I didn’t go crazy chasing after them. Ronnie was like, ‘Look, calm down.’ I worked extremely hard listening to my corner.

“ÔǪ I’ve proven to myself that I’m intelligent outside the ring. It’s about time I start showing it in the ring as well.”

Man of all people: Diaz said he has received rude lessons in the fierce pride Mexican nationals have in their fighters and learned from them.

The Mexican-American, whose parents both came to the U.S. illegally but are now citizens, said Mexicans – as well as Central Americans – constantly question his heart because he was born in the U.S.

“Ninety-nine percent of the time it comes from the Hispanic media, whether it be Mexicans, Salvadorans, Hondurans ÔǪ ,” he said. “They say, ‘You’re only 50 percent Mexican. ÔǪ Why do you think you can beat a 100-percent Mexican?’ I keep hearing it over and over. It kind of upset me. I said, ‘You know what? I don’t care. I don’t care what I am. I don’t care if I’m 25, 50, 100 percent Mexican. It doesn’t matter.’ And, really, one interview made me so upset I said, ‘I don’t even fight for the Mexican people.’

“When I went down there [to Cancun] to fight Nate Campbell, they all crowded around me wanting to take pictures with me, wanting autographs and what not,” said Diaz, who spoke Spanish to them. “Then they said, ‘Where were you born?’ ÔǪ I said I was born in Houston. They said, ‘Oh man, you ain’t Mexican.'”

Diaz was asked whether he believes American fans care as much about where a fighter is from.

“We don’t,” he said. “ÔǪ The cultures are so integrated together. Whether it’s a Hispanic fighter, a black fighter, a white fighter, people go and watch them and support them.”

Diaz, who has publicly criticized the controversial new immigration law in Arizona, believes many Mexican-Americans feel differently because of the way they’re perceived south of the border.

“I see a lot of Mexican-Americans who don’t oppose the law,” he said. “Why? Because when then go down to Mexico, they’re not treated the same, not treated equally. I think that’s why I don’t see a lot of Mexican-Americans speaking out against the law. They feel they’re not respected by the Mexican people when they go down there.”

Get your bets ready: Paul the octopus has a rival.

Paul is the German octopus who became world famous by correctly predicting the winner of Germany’s seven 2010 World Cup games and the Cup final. Now, an octopus at the Giant Shark Reef Aquarium at Mandalay Bay will attempt to predict the winner of Marquez-Diaz.

The second octopus, which Oscar De La Hoya dubbed “Oscar” at the news conference, will chose from two containers that each hold a mussel and are marked with the name of each fighter.

“We considered putting the fighters themselves in the tank but we didn’t think they could hold their breath long enough,” De La Hoya said.

The prediction will take place at 9:30 a.m. – or whenever the octopus feels like a meal.

Next up? Two fighters with a vested interest in the Marquez-Diaz fight – Amir Khan and Michael Katsidis – attending the news conference.

Khan, holder of a major 140-pound belt, will observe Ramadan from Aug. 11 to Sept. 9 and then get back to training. He gave a list of fighters he’d like to meet after that to Richard Schaefer of Golden Boy Promotions, his promoter. On the list: Marcos Maidana, Victor Ortiz, Timothy Bradley, Katsidis and the winner of the Marquez-Diaz fight.

Katsidis, Marquez and Diaz currently fight at 135 pounds.

“I spoke to Richard,” he said, “He’s going to give me the best package he can make, the best deal. And the best fight. I left it up to Richard. I’m going to enjoy Ramadan and take a month off before I start training.”

Khan was asked whether there is a specific fighter he’d like to meet. His response: Maidana, the hard-punching Argentine who some believe would exploit Khan’s supposedly fragile chin. The Briton was KO’d in one round by Breidis Prescott almost two years ago, his only loss.

“I’d love to fight him and shut people up,” Khan said. “I have the boxing skills I know can beat him. I have long arms, I hit and move. I don’t think he can cope with my speed and power. ÔǪ I think Michael Katsidis would make for a great fight as well. He has a style that would make for an explosive fight.”

Schaefer said it is unlikely that the 135-pounders would move up in weight. Thus, Maidana (promoted by Golden Boy), Ortiz (Golden Boy) and Bradley (Gary Shaw) are Khan’s most-likely opponents.

That would make Katsidis the most-likely candidate to face the winner of Marquez-Diaz, particularly because the Aussie is the No. 1 challenger for one of Marquez’s two sanctioning-body titles.

“I have my commitment with the WBO,” Katsidis said. “The winner of this fight must fight me within 120 days or be stripped. I’m more than happy to be world champion that way or fight the winner of this fight.”

Katsidis lost a split decision to Diaz in 2008 but has won four consecutive fights since. Would he like revenge?

“I think I’d get redemption against either one of these fighters,” he said. “If I beat Marquez, I don’t think anyone would ever question me again. If I beat Diaz, no one would question me again. I definitely would put a few people to silence.

“I’m on the up and up now. I’m a more-experienced fighter.”