At Monday's premiere at the Ziegfeld Theatre, Julia Roberts and Clive Owen were all smiles. But how sneaky are they in real life?

Owen, who plays Ray Koval, admits defeat when it comes to who would win in a battle of wits. "She would, because she's very smart," he says of his co-star.

Roberts, who wore Christian Dior to the premiere, agrees. "I would. It's just me," says the actress. "I have my tricks."

Paul Giamatti plays a scheming CEO in the movie and has a fight scene with Tom Wilkinson. Giamatti also concedes defeat if he and Wilkinson were to battle in real life.

"He has that sublimated British rage," Giamatti says. "He plays golf and has a new hip. He'd kill me."

The film was written and directed by Michael Clayton's Tony Gilroy.

Roberts' character, Claire Stenwick, is her first lead after a supporting turn as a Southern socialite in 2007's Charlie Wilson's War opposite Tom Hanks in the title role. And fans standing outside the theater greeted her return with deafening screams.

The Pretty Woman and Erin Brockovich actress addressed comments about her voluptuous physique in Duplicity. "I was nursing" during filming, says Roberts, whose son Henry is 1½.

And now that she can add Owen to her list of leading men — including George Clooney, Richard Gere, Hugh Grant and Brad Pitt — what does she think?

"I'm the luckiest girl in the world."