Claressa Shields showed her striking power as she stopped Brittney Elkin with a barrage of punches in the third round of her MMA debut in New Jersey.
The 26-year-old American, who is one of the biggest stars in women's boxing, overcame a difficult start to her career in the Professional Fighters League as she was forced to the ground for two rounds before delivering an explosive finish.
Shields switched her attention to MMA after becoming a two-time undisputed champion in March and Elkin pounded her with punches after gaining full mount in the opening round.
Elkin then withstood a flurry of shots in the second from Shields, who had to escape an armbar after again being forced down.
But Shields repelled another takedown attempt in the third, responding with a torrent of heavy shots before referee Gasper Oliver waved it off.
"I feel like I am dreaming," Shields told ESPN. "This is crazy."
"I never doubted myself winning a boxing match in my life. MMA, it's like it's possible I can lose this first fight.
"I just had a never-quit attitude every round.
"She had me on the ground, but she couldn't hurt me. Her punches didn't hurt me. She tried to get me in an armbar and that didn't hurt me.
"I may have lost these two rounds, but I'm not losing this fight."