Jessica Chastain is expected to be in a close race with herself at the box office this Martin Luther King Jr. holiday weekend. She stars in last week's No. 1 film, Zero Dark Thirty, and also stars in the debuting horror film Mama. Industry pundits say each film should wind up with around $20 million, with Mama likely to edge out Thirty. Also opening this weekend are two action flicks, Broken City, starring Mark Wahlberg and Russell Crowe, and Last Stand, which marks the return of Arnold Schwarzenegger to the screen in a starring role since 2003. Those films are expected to battle for third place with around $15 million. The holiday weekend also marks the nationwide expansion of the critically praised Oscar contender (it received eight nominations) Silver Linings Playbook. It's expected to take in around $10-15 million.