Film buffs might have recognized Michelle Monaghan's appeal in such movies as "Kiss Kiss Bang Bang," "North Country" and "Gone Baby Gone." But she hasn't had a chance to carry a movie until "Trucker," which had its world premiere at Tribeca and makes us realize what we've been missing.

Her performance elicits the same exhilarating sense of discovery that surrounded Sally Field's breakthrough in "Norma Rae." And there are some parallels between the two characters.

Monaghan's Diane is a bruised, ballsy woman who has made something of a mess of her life. She goes through a transformation during the course of the story and emerges as strong rather than merely tough.

Although "Trucker" doesn't have the social import that made "Norma Rae" a hit, it's an affecting, small film that could catch on with sophisticated audiences as well as more down-home types.

Monaghan plays a trucker who kisses off a typical one-night stand during the opening scene. She's a hard-drinking gal who likes her independence, but when her ex-husband (Benjamin Bratt) discovers he is terminally ill, Diane has to take charge of the son (Jimmy Bennett) she hasn't seen in years. Although there isn't much doubt where the story is heading, and though it could definitely use a few more surprises, the performances carry the movie. Writer-director James Mottern demonstrates both rigor and tenderness in his feature debut.

Monaghan shows absolutely no vanity in exposing the hard, reckless side of the character, and Bennett matches her. Already a veteran of a dozen movies, the youth exudes an unaffected ease that other child actors might envy. The strongest scenes come in the unsentimental tug of war between mother and son. Nathan Fillion is enormously likable as Diane's best pal who might have the potential to be something more. Although Bratt's role is underdeveloped, he gives dimension to his few scenes. The atmosphere of roadside Americana is genuinely portrayed, as well. The story might not be earth-shaking, but Monaghan's star-making performance assures that it will be remembered. (partialdiff)