A little curiosity went a long way to Gina Carano's transformation from mixed martial arts fighter and "American Gladiator" competitor to action-film star in "Haywire," the Steven Soderbergh film opening today.

"A few years back CBS was running the MMA fights on Saturday and I tuned in out of curiosity. That's where I saw her fight the first time and I literally thought, 'Why doesn't someone build a movie around her?' " director Soderbergh told the audience at Comic-Con International in July. "You've never seen someone perform like this ... in a cage! It was almost two years ago exactly I took the train [to San Diego] to meet her, to talk to her about being in a movie."

Ms. Carano was down in the dumps at the time, having lost a fight to Christiane "Cyborg" Santos that left her with a black eye. When her agent called to set up the meeting, she wasn't all that familiar with Mr. Soderbergh, director of "Traffic" and "Contagion," but she covered the black eye with makeup and picked him up at the train station.

"We had this amazing four-hour talk," she recalled. "Not so much about movies but about life and experiences. And at the end of it he said this is going to happen really fast or it's not going to happen at all. And it happened."

Soon, the fighter was running through the streets of Dublin and Barcelona, with Mr. Soderbergh tracking her from behind a camera lens. The story came together when the director called on his collaborator from "The Limey," Lem Dobbs, to write "a female revenge movie" that wound up as a web of espionage with a generous helping of epic fight scenes.

The director chose an all-star cast to surround the untried actress, including Antonio Banderas, Ewan McGregor, Bill Paxton and Michael Douglas. And he chose Michael Fassbender, an emerging superstar with credits including "X-Men: First Class" and "Shame," and the athletic Channing Tatum to go toe-to-toe with Ms. Carano, whose MMA-circuit nickname was "Conviction."

Mr. Tatum was already enamored with Ms. Carano's talent when he got the call for "Haywire." "I was in," he said. "I've been a fan of Gina's since I watched her on 'Girl Fight,' the reality show."

He might have regretted that decision because there were no stunt doubles for the fight scenes. He joked, "They might have had to calibrate her to pull back a little for us." She countered that Mr. Tatum "asked me to kick a little harder" in their shared scenes, which include the opening of "Haywire," a violent encounter in a diner.

"Her level of commitment is amazing," Mr. Tatum said.

"Our scenes are very athletic, it was almost like a dance, and I'm really athletic so it flowed very naturally," Ms. Carano said of working with Mr. Tatum, whose roles include the romantic "Dear John" and the title character in the G.I. Joe franchise. "And then there was a scene where [another fight with Mr. McGregor takes place] on the beach and struggling through sand and flopping all over the place, and that was really fun. And then of course the Fassbender scene was just reckless. I just loved hitting. ... That was a blast."

Perhaps not so much for the actor. "The Fassbender scene" is another brutal one-on-one fight, this time in a hotel room. Ms. Carano was supposed to clock the actor with a fake vase but accidentally grabbed the real thing and smashed him with it. She also got bumps and bruises from being thrown into a big-screen television.

"He laughed about it a little," Mr. Soderbergh said of Mr. Fassbender, and added that you'll see those moments in the film.

Mr. Tatum said his dance background helped him survive performing his own stunts opposite a woman who describes her first stint as an action-movie star as a "crazy adrenaline rush."

That dance background includes the Ricky Martin video for "She Bangs," the movie "Step Up" and some time spent making ends meet as an exotic dancer. That may make for a fun sketch when Mr. Tatum hosts "Saturday Night Live" Feb. 4.

His story has already inspired Mr. Soderbergh's next film about the world of male strippers. If you frequent Internet entertainment sites, you've probably seen the picture: Mr. Tatum, shirtless, flanked by Hollywood hunks Joe Manganiello, Matt Bomer and Matthew McConaughey, also shirtless, for the upcoming "Magic Mike."

They owe it all not to the women who swoon over such things, but to the woman who can kick their butts.

Mr. Tatum said the girl-guy fights in "Haywire" helped him settle an argument with his father.

The elder Tatum had long held that there was no place in film for a female action hero. He would tell his son, "Let me meet the female that can whup me and I'll watch the movie."

"I told him that Gina was the real deal," Channing Tatum said. "She simply has this incredible skill set, and that's what [her character] Mallory is in the movie. She's smart, she's tough and she's lethal."

First Published: January 20, 2012, 10:00 a.m.