Minka Kelly and Leighton Meester's new thriller "The Roommate" has scared up big business at the box office - the film has debuted at number one.
 
The movie took in $15.6 million in its opening weekend to finish well ahead of director James Cameron's latest 3D offering "Sanctum," which scored a weak $9.2 million first weekend take.
 
Last week's number one movie "The Rite" drops to six, while romantic comedy "No Strings Attached" rounds out the new top three.