Murodjon Akhmadaliev made sure Friday night to finally secure the legacy-defining fight he has long wanted.

The former IBF/WBA 122-pound champion moved toward a showdown with Japanese superstar Naoya Inoue by stopping Mexican underdog Luis Castillo in the eighth round of a tune-up fight at Domo Alcalde in Guadalajara, Mexico.

Akhmadaliev (14-1, 11 KOs), a southpaw from Uzbekistan, dropped Castillo once apiece in the fifth and sixth rounds before assaulting him with a barrage of punches that prompted his trainer to throw in the towel.

Referee Luis Jimenez officially stopped the bout at 2:05 of the eighth round.

Akhmadaliev's victory guaranteed his shot at Inoue's Ring, IBF, WBA, WBC and WBO 122-pound championships Sept. 14 in Osaka, Japan. Inoue, 32, and Akhmadaliev, 30, signed contracts to fight in 3½ months before Friday night's fight.

Akhmadaliev took a measured approach to his relatively easy fight with Castillo and seemingly could've ended it before he did.

He eventually ensured what he wanted two years ago. Akhmadaliev expected to challenge Inoue by now, but the Philippines' Marlon Tapales upset him by split decision in April 2023 at Tech Port Arena in San Antonio, Texas.

Inoue (30-0, 27 KOs), who is ranked No. 2 on The Ring’s pound-for-pound list, knocked out Tapales in 10th round eight months later at Ariake Arena in Tokyo.

Castillo (31-7, 20 KOs), who was born deaf and non-verbal, slipped to 2-4 in his past six fights. He also lost inside the distance for the second time in 10 years as a pro.

Before Akhmadaliev hammered Castillo with power punches during the eighth round, his hard left to the head knocked him down with 58 seconds to go in the sixth. A courageous Castillo beat the count for the second time in as many rounds and reached the seventh.

A left to the body by Akhmadaliev sent Castillo to his hands and knees with just under 10 seconds to go in the fifth. Castillo beat the count.

Akhmadaliev got off to a slow start. After two mostly unmemorable rounds, he landed a straight left that knocked Castillo off balance with 1:15 to go in the third round.

Akhmadaliev also stepped on Castillo's foot as he landed that punch, which might've prevented him from following up.

Akhmadaliev also appeared to hurt his left hand when he landed that flush punch and had to shake it off for the remainder of the third and during the fourth.

Akhmadaliev drilled Castillo with a left to the body that seemed to send him to the canvas late in the fourth. It was not counted as a knockdown, though he later was credited with two knockdowns.