In the very first scene of David Fincher's "The Social Network," Rooney Mara quells any doubt that she's qualified to play Lisbeth Salander in Fincher's version of "The Girl with the Dragon Tattoo." As a woman who decides that she can no longer date a bundle of insecurities and ambitions named Mark Zuckerberg (Jesse Eisenberg), she anchors the entire film with her decency and sanity and trust in her own instincts. All the other characters, at one time or another, over-value mere brilliance. Mara and her character bring the movie rare emotional intelligence. She's under a lot of pressure as a performer here -- in just a few minutes she must operate as a flesh-and-blood Rosebud in a film that is the 'Citizen Kane' of the Facebook generation. But Mara pulls it off. It isn't a showy role but it's a crucial one, and for my money Mara embodies it as superbly as Judi Dench did Queen Elizabeth in "Shakespeare in Love." (In other words, award-givers should ignore the brevity of the part and take note of Mara's mettle.) Those who worried about Mara playing Salander should now be avidly anticipating what she can do under Fincher's direction in the plum female role of the decade.