LAS VEGAS — Gary Russell Jr. didn’t look like a boxer who hadn’t fought in almost 3½ years Saturday.

The former WBC featherweight champion outclassed Hugo Castaneda with his hand speed, skill, power and athleticism, dropped him four times and knocked him out with a body shot early in the 10th round at MGM Grand Garden Arena. Referee Harvey Dock stopped their scheduled 10-rounder 26 seconds into the final round on the Manny Pacquiao-Mario Barrios undercard.

Russell, 37, hadn’t fought since January 2022, when the Philippines’ Mark Magsayo upset him by majority decision to take the WBC 126-pound championship from the 2008 U.S. Olympian. The left-handed Russell (32-2, 19 KOs), of Capitol Heights, Maryland, entered that bout at Borgata Event Center in Atlantic City, New Jersey, as boxing’s longest-reigning champion.

A lingering shoulder injury and focusing on training his younger brothers, including WBA 140-pound champ Gary Antuanne Russell, kept him out of the ring for three-plus years. His knockout of Castaneda (15-3-1, 11 KOs) marked just the seventh fight for the notoriously inactive Russell since he stopped Mexico’s Jhonny Gonzalez in the fourth round to win the WBC featherweight title in March 2015.

Russell drilled Castaneda with a left to the body that knocked him to his gloves and knees 13 seconds into the 10th. The game Mexican beat Dock’s count for the fourth time in their bout, but he was too hurt for Dock to allow him to continue.

After getting dropped twice in the second round and once in the sixth, Castaneda let his hands go in the third and seventh rounds. Russell covered up, blocked punches, tied up Castaneda and never appeared bothered.