Greta Gerwig, Noah Baumbach: Big Films, Big Romance and the Secrets to Making It all Work

— -- Could it be that Greta Gerwig and Noah Baumbach's romantic chemistry is the key to their big screen success?

The creative duo has co-written and just released the new movie "Mistress America," their third film with Baumbach as director and Gerwig as the star. This time Gerwig plays the role of Brooke Cardinas, who Gerwig describes as a "gal about town".

"We wanted to do something together again and I think really we had no idea what that was. We just started talking and this character became Brooke Cardinas," Baumbach told ABC News.

"And Greta was just so funny doing it, even just saying the lines as we were writing them, that we decided that it would be kind of a great character for her to play. And we just had to come up with a movie that would support this character. So really this movie is one big excuse to fit that character into something," said Baumbach.

Some might think living together and working together 24/7 might present unique challenges for the couple, dating since late 2011. But Gerwig told Peter Travers their personal relationship actually fuels their creative process. When they're collaborating on a film, they use their time at home to focus more on the project at hand.

"I think we tend to only talk about the movie," Gerwig, 32, said. "It's nice when it's the same movie, when we're working on the same movie. Then we can get home and sort of hash out what the day was and what the next day will be. So I like being completely absorbed in a project."

"You don't have that much down time," Baumbach, 45, added. "You're shooting fairly long days. You sleep. You get up early and you start over. So in a way you're in this like, it's a bubble, it is a bubble."

It's a system that works for them. Together Baumbach and Gerwig penned the 2013 critically acclaimed comedy "Frances Ha." And in 2010, Gerwig starred in Baumbach's award-winning comedy "Greenberg."

"Mistress America" is in theaters now.