LAS VEGAS -- Vasyl Lomachenko successfully defended his WBO junior lightweight title, winning when Nicholas Walters was unable to continue after seven rounds Saturday night at the Cosmopolitan.

Lomachenko, the 28-year-old Ukrainian star who won two Olympic gold medals, improved to 7-1. Lomachenko dropped to 26-1-1.

"My goal is to be the No. 1 pound-for-pound fighter in the world," Lomachenko said.

Lomachenko had his best round of the fight in the seventh, landing multiple power shots, including a hard shot to the temple that ultimately led Walters to stop fighting.

"He's a good fighter, really strong," Lomachenko said. "But he stood there and made it easy for me, then in the end he just quit."

The pace quickened in the third, with Lomachenko leading the action and Walters looking to counter. Lomachenko landed a hard straight left, the best punch of the fight up until that point and began to establish himself as the aggressor by the end of the fourth.

Walters battled back in the fifth landing a few power shots, only to be matched by Lomachenko combination for combination.

"He's a great fighter," Walters said. "He's very fast, a great puncher. He caught me with a hard shot to the temple."

Lomachenko began to take control in the sixth, displaying superior technical skills and controlling the ring. By the end of the seventh, Lomachenko had the fans on their feet as he looked to finish the fight, landing a number of powerful combinations.

Walters survived the flurry and appeared fine as the round ended and he headed back to his corner. However, between rounds, Walters' corner informed the referee that he was unable to continue and the fight was stopped and ruled a TKO for Lomachenko.

Lomachenko captured his first word title, the IBF featherweight crown, in just his third fight. That tied a record for the fewest fights needed to win a championship. He defended the belt three times before winning the junior lightweight title, earning his second title in as many weight classes.