CARSON, Calif. — Brian Castano crumbled in a heap, the product of a right hand to the body followed by a left hook to the head from Jermell Charlo in Round 10 of an instant classic Saturday at Dignity Health Sports Park.

Somehow, someway, Castano made it to his feet before the count of 10, but his courage was simply a precursor to the swift end. The Argentine was in no shape to continue, and Charlo sensed the moment.

He sprinted over to Castano and unleashed a series of lefts and rights that floored Castano one final time, then headed to the turnbuckle to celebrate as the referee counted to 10 with seven seconds remaining in the round.

Now, after 12 rounds couldn’t separate them in a July draw, the junior middleweight division has an undisputed champion and his name is Jermell Charlo.

“This is unbelievable,” said Charlo, who was ahead 87-84, 88-83 and 89-82 entering Round 10. “I gave it my all. It was nerve-wracking. It felt like my first fight. I knew Castano was going to give it his all. … I wanted to make sure it was my fight. … The future is bright.”

Charlo becomes the ninth undisputed male champion in the four-belt era.

Castano said through a translator: “Everything that happened here, we showed we’re warriors tonight. We both were fighting back and forth, it was power back and forth, and then his [left] hand ended the fight.”