The 39-year-old, an Olympic bronze medallist in judo in 2008, wasted no time when the fight began at the Intuit Dome in the first MMA card staged by Jake Paul's Most Valuable Promotions. She took down the 44-year-old Carano, quickly moving into position for the armbar, forcing her opponent to tap out quickly or risk her arm being broken.
It is a submission that became Rousey's signature move during her dominant reign as UFC bantamweight, and even though Carano, who was fighting for the first time in 17 years, knew it was coming, there was little she could do to stop it.
"Gina is the person who brought me into MMA, she's the only person who could have brought me back into MMA," a delighted Rousey said in her post-fight interview before addressing her opponent.
"You brought me back home... you changed my world, and we changed the world. And I will never ever forget, and I will never be able to pay you back enough. I'm so glad we finally got to share this moment."
Carano was disappointed that the bout ended so quickly, but after more than a decade and a half out of the cage as she built an acting career, she said that just making it to the fight was an achievement.
"I wanted that to last longer. I felt like I was so ready. I felt so good. I've never felt that good, but I haven't been here for 17 years, so I mean, I wanted to. I wanted to hit her," she said.
"You feel a little unfulfilled, just because you didn't get a chance to at least show the world what you've been working on, you know. I'll probably feel that later. Right now, getting in the cage was a victory. Getting here after 17 years is a victory."
In the evening's co-main events, lineal heavyweight champion Francis Ngannou knocked out Philipe Lins in devastating fashion, and Mike Perry opened up some gruesome cuts on fan favourite Nate Diaz to secure a second-round stoppage win.