"Oh, yeah, let's get the 'Legally Blonde' guy to do a Vegas heist film" — that was the initial, dismissive response, Robert Luketic recalls, when he started pitching himself as the perfect candidate to direct "21."

Here he was, a little-known Aussie with a surprise Reese Witherspoon hit and the lighter-than-air Kate Bosworth rom-com "Win a Date With Tad Hamilton" to his credit, presenting himself as the man to pull off the taut, true-life tale of a bunch of M.I.T. brainiacs who figured out how to beat the house in Las Vegas.

"It was very liberating for me to be given a chance to do this," Luketic says, on the phone from his adopted home of Los Angeles. "I was very frank and honest with myself, my name's not the first that comes to mind when you think of this genre, given the kind of movies that I've done before. ...

"This was really something I had to fight for — it was almost like going back to being a first-time filmmaker again: get in the room and really prove that you were right for the job, which wasn't easy."

But he did just that, explaining to the powers-that-be — including Kevin Spacey, who plays the students' M.I.T. prof in the pic, and who also produced the project — that he knew how to make the blackjack sequences exciting for viewers.

As anyone who has dozed off during the long card-playing sequences in "Casino Royale" can attest, a deck of diamonds and clubs, hearts and spades does not a riveting piece of cinema make.

"I talked about how blackjack wasn't a spectator sport, but how I would make it visually compelling," says Luketic (lou-KET-ick).

"21" is adapted from the book "Bringing Down the House," Ben Mezrich's expansion of an article he wrote for Wired magazine about a group of math whizzes from the Massachusetts Institute of Technology who, back in the '90s, came up with a system to beat the odds at blackjack and take the casinos for millions.

Luketic cast Jim Sturgess as the group's chief numbers man. Bosworth, Laurence Fishburne, Liza Lapira, Jacob Pitts and Aaron Yoo also star.

Luketic, 34, read the Wired article when it came out in 2001. "I was struck by what a great idea for a movie this would be, and the fact that it was a true story," he says. "There was nothing particularly special about card counters, they'd been around for a while — as long as Vegas has existed, people have tried to work a scam or an angle. But what was fascinating was the complex system of body language and words they employed, and the way that it was made into a team effort. ... And that these kids actually, really did change the system, they fundamentally changed the rules by which casinos now operate today. They had a real impact, they were major players.

"I also loved the notion of a group of nerds inheriting the keys to Las Vegas. There was something very appealing about that."