By Keith Idec

Joseph Diaz Jr.’s upper body shook as he flexed his muscles at a weigh-in Friday afternoon.

The undefeated southpaw hopes to shake up the featherweight division Saturday night by beating Gary Russell Jr. The taller Diaz thinks his 1½-inch height advantage and an expected weight advantage in the ring will serve him well when they fight for Russell’s WBC 126-pound championship at MGM National Harbor in Oxon Hill, Maryland.

The 29-year-old Russell (28-1, 17 KOs), of nearby Capitol Heights, Maryland, officially weighed in Friday at 125½ pounds for their scheduled 12-round championship match. The 25-year-old Diaz (26-0, 14 KOs), of Downey, California, stepped on the Maryland State Athletic Commission’s scale exactly at the featherweight limit of 126 pounds.

Russell is consistently listed as about a 3-1 favorite over Diaz, who expects to shock plenty of people Saturday night.

“You’ll see Saturday night,” Diaz told Showtime’s Steve Farhood following their weigh-in. “Saturday night, I’m gonna be the bigger man in there. I made the weight. Now it’s time to go and hydrate. Training went well. My conditioning is good. My strength’s there. I’ll be the bigger man. I’ll walk down Gary Russell, break him down physically and mentally. I’ll be the new champion come Saturday night, baby.”

Diaz acknowledged that Russell, also a southpaw, is the fighter with faster hands and feet.

“I respect his speed, but at the end of the day speed’s not gonna beat everything,” Diaz said. “You have to have the right timing, and I have the right timing. And I’m able to adapt and adjust to any style. And you’re gonna see that come Saturday night. Gary Russell Jr., he is fast and I respect that. We’re gonna give the fight fans a hell of a fight.”

Russell, a 2008 Olympian, will end almost exactly a one-year layoff when he encounters Diaz.

He hasn’t fought since last May 20, the night he stopped Colombia’s Oscar Escandon (25-3, 17 KOs) in the seventh round at MGM National Harbor. Russell has defended his WBC featherweight crown just twice since scoring a fourth-round technical knockout against Mexico’s Jhonny Gonzalez (66-10, 54 KOs) to win it in March 2015.

Showtime will air Russell-Diaz as the opener of a split-site doubleheader at 10:05 p.m. ET. The two-bout broadcast will continue from Toronto, where WBC light heavyweight champ Adonis Stevenson (29-1, 24 KOs) will defend his title against Badou Jack (22-1-2, 13 KOs) at Air Canada Centre.

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