The 39-year-old Rousey ended a nine-and-a-half year absence from MMA when she took the cage with the 44-year-old Carano, who hadn't fought in 17 years.
Rousey (13-2) wasted no time when the door finally closed, charging and tackling Carano an instant after the opening bell rang.
- Harrison on retiring, his legacy and the wildest round in combat sport
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Rousey quickly moved into position and applied her famous finishing move, wrenching Carano's arm as the fight was stopped.
"I really didn't want to hurt her," Rousey said. "Luckily it was just beautiful martial arts, that's what it is."
Rousey famously won eight fights in less than a minute during her meteoric rise through MMA in the 2010s. When asked if she considered waiting a bit longer to go for the finish in a fight so many years in the making, Rousey laughed.
"Hell no," she said. "My husband and my kids are watching me. I don't want to put them through anything more than I have to."
Carano was all smiles even after the swift end to one of the longest layoffs in pro sports history. Rousey and Carano hugged and shared warm words after the finish.
"I felt so ready," Carano said. "I've never felt that good. But I haven't been here for 17 years ... and I wanted to hit her."
This improbable double comeback bout united two of the most important fighters from MMA's past two decades.
Rousey became one of the world's most famous athletes as she won the first women's title in the UFC, which only began to promote women's MMA because of Rousey's undeniable talent and star power.
Rousey first became interested in MMA because of Carano, whose athleticism and star power made her into a television headliner when the sport was still fighting for legitimacy and acceptance in the late 2000s.
Carano was happy to finally accept the comeback she had occasionally considered, saying she used her preparations as a way to overcome multiple health problems from recent years.
Rousey has repeatedly said this will be her final fight, while Carano has said she doesn't know what the future holds.
