The films of John Cassavetes have quite a bit in common, thematically and aesthetically, with one of the most famous and most obvious being the function of actors in his style. In a Cassavetes picture, performance isn't necessarily important because of how it reveals character, but because of how it reveals the process of performing: it's never clear in something like A Woman Under the Influence, to take one well-described example, whether we're responding to the torments of Mabel and Nick Longhetti, or to the torments of Gena Rowlands and Peter Falk in playing Mabel and Nick.

This thread of Cassavetes's work reaches what must surely be its peak in his 1977 Opening Night, in which Rowlands plays Myrtle Gordon, an actress finding it virtually impossible to get into her new role as "Virginia", the menopausal heroine of a play called The Second Woman, in try-outs in New Haven. A long-ignored note in the director's career of poorly-distributed films (its New York premiere wasn't until 1991, two years after his death), Opening Night is as densely layered and difficult as anything else Cassavetes had directed, as dense as any American film from the 1970s, but it all starts with the extraordinary central performance, and the manner in which the film blurs the line between Myrtle, Virginia and Rowlands herself: acting is being, and all three women seem to occupy the same space for most of the movie.

I've given myself too easy a segue not to use it: there are two sets of three women in the film, the other being Myrtle, the elderly playwright Sarah Goode (Joan Blondell, whose 40-year career is probably best known for her work in several of Busby Berkeley's musicals at Warner in the '30s) who wrote The Second Woman as her own meditation of aging, and Nancy Stein (Laura Johnson), the 17-year-old girl who haunts Myrtle's imagination after the actress sees her die in a car accident on a rainy night after standing at the stage door for an autograph. It's a tempting oversimplification to claim that metaphorically, all three of these characters are one woman at three stages of life; that is certainly the way that Myrtle views their relationship, but "how Myrtle sees the world" and "how Opening Night sees the world" aren't synonymous positions. For one thing, that simple maiden-matron-crone breakdown ignores that there's a lot more to Sarah than just being a worn-out old lady, not to mention how rudely it treats poor Nancy: we never know a thing about her other than that she is star-struck, but to Myrtle, she represents everything wonderful about youth, and in order to make her own breakdown complete, it is necessary that she pulls Nancy back from the dead to fulfill a three-part structure that exists only in Myrtle's own mind.

One could explain Myrtle's conflict in pretty simple terms that would pull a little bit of the magic out of the movie, basically that she is already worried about aging, and seeing a young girl's life snuffed out right at the same time that she's struggling with her part pushes her too far. Her great fear, contra what some including Sarah and the director Manny Victor (Ben Gazzara, like Rowlands a frequent face in Cassavetes's cinema) think, is not that she is already like Virginia, but that she is going to turn into Virginia, and that "becoming" the character onstage means becoming the woman in reality. Leading to her quixotic attempt to play the part without any reference to aging, a typically Cassavetean touch of noble insanity; after all, how could one ever play the lead in The Second Woman, whose very title is seemingly about menopause (though we never have a very clear sense of what the play's story is about, or if it's remotely good), without reference to age?

I say this reading robs Opening Night of some of its magic, because it reduces the film to a simple and clichΓ©d matter of women of a certain age realising that the world only like pretty girls, which is at best a portion of the movie, hardly the complete picture. Though the specific case that the story looks at is a woman afraid that her part will turn her into an old lady, the more general idea is what happens to an actor who cannot believe the basic truth of her role - how can you get inside the human core of something that is basically just a stereotype reflecting some author's limited imagination about people? At one point, an exasperated Sarah tells Myrtle to "say the lines, with some inflection of emotion, and Virginia will appear," a gross reduction of the art that even Myrtle is clear-headed enough to view with precisely the disdain it deserves.

Nor does her director Manny have anything remotely useful to provide, apparently guessing that when you cast a "super-high-priced professional",* the good acting takes care of itself. Dealing with the third-act slap that is perhaps Myrtle's single greatest problem with the play, delivered as it is by her ex-lover Maurice Aarons (Cassavetes himself, in a role given much extra bite from the viewer's knowledge that he and Rowlands were happily married 22 years at this point, and would be until his death). Manny's advice: "It's a tradition, actresses get slapped." When Myrtle finally discovers how to play that moment in a way that doesn't shame her as a person and a woman, it's a scene that destroys the play and even starts to corrode the fourth wall of the movie: watching Virginia and her lover turn into Myrtle and Maurice, we're also watching Myrtle and Maurice turn into Rowlands and Cassavetes, neither of whom try very hard to keep in character - which character? - as the audience starts cracking up. An audience which was brought in live and given no indication of what has happening, mind you, other than that they were about to see scenes from a play being work-shopped.

The film is a masterpiece, unjustly ignored for too long and still far more obscure than it should be, relative to equally great works like A Woman Under the Influence, The Killing of a Chinese Bookie and Faces. Giving Gena Rowlands, one of the best actresses who ever walked in front a camera, a chance to work out her process on film may or may not have been a generous thing for her, but it proved to be an absolutely brilliant gift to the audience. Opening Night does more to break down the walls between layers of narrative; between who the characters are, what they do, who plays them; than just about any American film I can name.