Jermell Charlo stops Brian Castano to become undisputed super welterweight champion

Jermell Charlo became the first first undisputed super welterweight champion in history on Saturday after knocking out Brian Castano in the 10th round of a thrilling fight in Los Angeles.

Charlo, the reigning WBC, WBA and IBF champion, earned Castano's WBO belt with the win at the open-air Dignity Health Sports Park arena. The American fought to a controversial draw against Castano last year.

The 31-year-old Charlo sent Castano to the canvas twice in the 10th round just as he had begun to get on top of a hard-fought battle that saw the two men share the opening rounds.

A crunching right hook to the body stunned Castano and Charlo followed with a left hook to the head that sent the previously undefeated Argentinian crumpling to the canvas.

With Castano unsteady on his feet, Charlo moved in to finish his opponent. A powerful left snapped Castano's head back and another punishing left to the body sent him to the deck for the final time.

"This is unbelievable," said Charlo, who improves to 35-1-1 (19 knockouts). "I gave it my all and that was the end result of it. This was nerve-wracking. It felt like my first fight, where you get nervous. I knew Castano was going to give it his all, and I trained very hard. I was in great shape."

Charlo's win elevates him to an exclusive club of fighters. He is only the seventh boxer to hold all four belts from the major sanctioning bodies – WBC, WBA, IBF and WBO – at the same time.

The six men to do it before are Bernard Hopkins (middleweight), Jermain Taylor (middleweight), Terence Crawford (super lightweight), Oleksandr Usyk (cruiserweight), Josh Taylor (super lightweight), and Saul 'Canelo' Alvarez (super middleweight).

Charlo and Castano's first clash in Texas last July ended in a