SAN ANTONIO – Three judges from outside of Texas and Argentina have been assigned to score the Jermell Charlo-Brian Castano 154-pound title unification fight Saturday night.

BoxingScene.com has learned that the Texas Combative Sports Program has chosen Nevada’s Tim Cheatham, Puerto Rico’s Nelson Vazquez and New Jersey’s Steve Weisfeld to judge the Charlo-Castano clash. A referee from Panama, Hector Afu, has been assigned to work their 12-round, 154-pound championship match at AT&T Center as well.

Charlo (34-1, 18 KOs), the IBF/WBA/WBC champion, is a native of Houston. Castano (17-0-1, 12 KOs), the WBO champion, hails from Buenos Aires, Argentina.

Cheatham and Weisfeld are two of boxing’s most experienced judges in high-profile fights. Vazquez works fewer televised championship bouts in the United States, but he has judged numerous title fights and has been a professional judge since 1987.

Afu typically officiates fights outside of the U.S., primarily in Panama.

Showtime will broadcast Charlo-Castano as the main event of a “Showtime Championship Boxing” tripleheader scheduled to start at 9 p.m. ET and 6 p.m. PT from the home arena of the NBA’s Spurs.

Unless their fight results in a draw, the Charlo-Castano winner will become boxing’s first fully unified 154-pound champion during the four-belt era and just the sixth such champion in any division. Retired middleweights Bernard Hopkins and Jermain Taylor, junior welterweights Terence Crawford and Josh Taylor and cruiserweight Oleksandr Usyk are the only boxers who’ve earned that distinction.

Most Internet sports books list Charlo as more than a 2-1 favorite over Castano.

Showtime’s tripleheader also will include a 12-round, co-featured bout between Las Vegas’ Rolando Romero (13-0, 11 KOs) and Sweden’s Anthony Yigit (24-1-1, 8 KOs) for Romero’s WBA interim lightweight title. The three-bout broadcast will open with a 10-round middleweight match in which Uruguay’s Amilcar Vidal (12-0, 11 KOs) will meet Immanuwel Aleem (18-2-2, 11 KOs), of Richmond, Virginia.

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