Matt Korobov was lined up for an eight-round fight against Juan De Angel on the off-TV undercard Saturday in Brooklyn.

That fight was contested at 162 pounds. One week before the fight, six days before the weigh-in, Korobov was presented an opportunity to replace Willie Monroe Jr. in the FOX main event against Jermall Charlo (Monroe tested positive for a banned substance.)

Korobov didn’t hesitate: he accepted the fight on short notice, and on Friday, weighed in under the 160-pound limit at 159.8. Like his opponent, Jermall Charlo (159.6 pounds), Korobov showed off an impressive physique.

Jermall, too, must adjust on short notice. Though they’re both southpaws, Monroe is a boxer who likes to fight at range; Korobov is a pressure fighter. “It hasn’t affected me,” he said. “I’m ready for this. I’m born for this. This is what I do.”

Jermall’s twin brother, Jermell, defends his WBC junior middleweight title in the co-feature against Tony Harrison. Jermell weighed 153.6 pounds, and Harrison tipped the scales at 153.8 before they began jawing at each other.

“I’ve been here before, I’ve does this before,” Jermell said angrily. “He know what I come to do. I know what I come to do. I’m ready.”

Harrison recounted what he told Jermell: “You’re finally up against somebody who’s credible, just as fast, just as strong and I’m bigger.”

Heavyweight contender Dominic Breazeale opens up the PBC on FOX telecast at 8 p.m. ET with a 10-round bout against Carlos Negron. Breazeale weighed 256.6 pounds. Negron weighed 226.

Mike Coppinger is the Senior Writer for RingTV.com. Follow him on Twitter: @MikeCoppinger