By Keith Idec

Jermall Charlo contends that a switch of opponents less than a week before his fight Saturday night hasn’t negatively affected him.

Houston’s Charlo, 28, officially weighed 159½ pounds, the same amount the Russian-born Korobov weighed when he stepped on the New York State Athletic Commission’s scale.

Korobov (28-1, 14 KOs) took this difficult fight on just six days’ notice. He replaced Willie Monroe Jr. (23-3, 6 KOs), of Rochester, New York, once Monroe tested positive for a “steroidal substance,” according to a statement released Monday by the Voluntary Anti-Doping Association.

The 35-year-old Korobov, of Lantana, Florida, was already training for a non-televised, eight-round fight on the Charlo-Monroe undercard against Colombia’s Juan DeAngel (21-9-1, 19 KOs). Korobov, like Monroe, is a southpaw.

Charlo (27-0, 21 KOs) will make the first defense of the WBC interim middleweight championship he won by knocking out Hugo Centeno Jr. (26-2, 14 KOs, 1 NC) in the second round April 21 at Barclays Center.

The two boxers scheduled to compete in the co-featured fight Saturday night made weight a few minutes earlier Friday afternoon.

Jermall Charlo’s twin brother, Jermell Charlo (31-0, 15 KOs), weighed in at 153½ pounds for the fourth defense of his WBC super welterweight title versus Tony Harrison. Detroit’s Harrison (27-2, 21 KOs) also came in at 153½ pounds.

Houston’s Jermell Charlo, 28, is consistently listed as a 12-1 favorite over Harrison, also 28.

Before Jermell Charlo and Harrison stepped on the scale, heavyweights Dominic Breazeale (19-1, 17 KOs) and Carlos Negron (20-1, 16 KOs) weighed in for their 10-rounder.

The 33-year-old Breazeale, of Eastvale, California, officially weighed 256½ pounds, 30½ pounds more than Negron. The 30-year-old Negron, of Villalba, Puerto Rico, stepped on the NYSAC’s scale at 226 pounds.

Numerous Internet sports books have listed the 6-feet-7 Breazeale as a 50-1 favorite over the 6-feet-6 Negron. Breazeale will risk his status as the mandatory challenger for WBC champion Deontay Wilder (40-0-1, 39 KOs) by boxing Negron, a 2008 Olympian.

The Breazeale-Negron encounter will be the first of three fights FOX will televise, starting at 8 p.m. ET/5 p.m. PT.

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