Entertainment Tonight ET Online ETOnline.com

Gerard Butler and Jessica Biel co-star in the romantic comedy Playing For Keeps, and according to Gerard, the chemistry is definitely there between the two of them.

"This is the best performance I've ever seen Jessica give," he tells ET at the film's New York City premiere Wednesday night. "It's really touching, it's very funny, it's full of angst -- and I felt that in every scene with her, you know? And she was so incredible to act with, and we got on really well. We became good friends and we had a lot of rehearsal time beforehand, so whenever we would do any scenes you just kind of felt magic between us, and you're feeling so many different things."

Video: Biel & Butler Talk Weddings & Women

Jessica echoes the pair's strong bond.

"I think we were both just so invested in this project and open to just whatever [director] Gabriele [Muccino] wanted from us, and that's the best way to come into a project. And the best way to interact with another actor is to just be open and excited about the work that you're doing together, and I think we both shared that," she says.

Jessica also gets to play a mom in the film, and she confesses that her latest role did have her thinking about having kids in real life with husband Justin Timberlake.

Pic: Gerard Butler Flaunts It in 'For Keeps'

"I think every role you play, somehow you start to think about in terms of your own life," she reveals. "And I was so lucky because Noah [Noah Lomax, who plays her son in the film], he's the most lovely guy and made my job so easy, and definitely made me want to be a mom to someone like that."

Check out the video to see the adorable Noah, 11, admit that he didn't know who Gerard and Jessica were before shooting the film. Playing for Keeps hits theaters December 7.