Jennifer Aniston Drums Up Oscar Buzz in Cake: Watch This Exclusive Clip
11/12/2014 AT 12:00 PM EST
"With this performance, Jen just let herself go raw in every way, emotionally and physically," Cake director Daniel Barnz tells PEOPLE of the role, which called for the usually glam Aniston, 45, to wear a back brace and sport facial scars.
"The first time we met, we talked about how this is a woman who actively doesn't take care of herself, who doesn't put on a stitch of makeup, who just completely lets herself go," he adds. "Because if the actress tried anything – a dab of lipstick, a tiny bit of mascara – it wouldn't be true to the character and the audience would cry foul."
Aniston's breakout performance has generated Oscar buzz since Cake premiered at the Toronto International Film Festival in September, and the film, which costars Anna Kendrick and Sam Worthington, will have an awards-qualifying limited run on Dec. 31.
Barnz, for one, was thrilled with Aniston's commitment from the start. "I always wondered how hard this would be for Jen, but she never wavered," the director says. "In fact, I think she found it quite liberating. But not wearing makeup is just the tip of the iceberg – what's really brave is how she exposes herself emotionally."
Check out PEOPLE's exclusive clip from Cake, which opens wide in January.