By GREG BEACHAM
AP Sports Writer
CARSON, Calif. (AP) — Jermell Charlo became the first undisputed super welterweight champion in the four-belt era when he stopped Argentina’s Brian Castaño in the 10th round of their rematch. After an outstanding bout with ample toe-to-toe action, Charlo dropped Castaño twice in rapid succession in the 10th. Charlo leaped onto the ropes in celebration while the referee was still counting out his opponent, celebrating the addition of Castaño’s WBO 154-pound title to his WBC, WBA and IBF belts. Charlo survived several impressive early rounds by Castaño in the rematch of the fighters’ split draw 10 months ago in Texas.