By Keith Idec, photo by Rich Kane/Hoganphotos

NEW YORK – Oscar De La Hoya was surprised just how much bigger Julio Cesar Chavez Jr. is than Canelo Alvarez the first time he saw them stand next to each other this week.

Their size difference figures to be at least as noticeable when the Mexican stars enter the ring May 6 at T-Mobile Arena in Las Vegas. The 6-feet-1 Chavez (50-2-1, 32 KOs, 1 NC), who has fought as high as light heavyweight, expects to be 180 pounds on fight night, 15½ more than the contracted catch weight for their HBO Pay-Per-View main event.

The 5-feet-9 Alvarez (48-1-1, 34 KOs) doesn’t know what he’ll weigh on fight night, but he doesn’t anticipate Chavez’s size advantage becoming more of a factor once the opening bell rings than Alvarez’s advantages in speed and skill.

“I knew it,” Alvarez said Tuesday before a press conference at the Hard Rock Café in Manhattan to promote their fight. “It’s written. He’s [four inches] taller than me. That doesn’t bother me, doesn’t worry me at all.”

The 26-year-old Alvarez has not weighed in at more than 155 pounds for any of his 50 professional fights. He expects, however, that he’ll push the weight limit of 164½ when he gets on the scale May 5 in Las Vegas.

The Mexican superstar wouldn’t estimate how much he’ll weigh when he enters the ring. The only thing he knows for sure is that it’ll be less than the 180 pounds Chavez expects to weigh.

“I can’t tell you right now how I’m gonna feel come fight night,” Alvarez said. “We’re gonna work with sparring partners that are gonna be heavier and bigger than me, so that we can start adapting to it. And I can tell you one thing, that in my training, in my camps, when I’m weighing between 160 and 165 is when I feel the best. So we’ll see come fight night.”

The 31-year-old Chavez believes Alvarez is underestimating how much Chavez’s size advantage will affect the outcome of their 12-round bout. He’s not fighting a natural welterweight like Amir Khan or a junior middleweight like Liam Smith, and Chavez knows Alvarez will be surprised by his opponent’s strength once Chavez starts hitting him.

“I’ll try to use my natural advantages – my size, my distance,” Chavez said. “And, you know, Canelo is moving up 10 pounds. He’s never felt the power of a light heavyweight or a super middleweight.”

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.