Once in a while a movie comes along that doesn’t just affect how you think or feel, it performs its own kind of physical alchemy, burrowing its way into your consciousness so thoroughly that you feel permanently marked and changed.

Blue Is the Warmest Color,” Abdellatif Kechiche’s long, sprawling, boldly immersive coming-of-age drama, works just this sort of magic. A naturalistic portrait of the sexual and romantic awakening of a teenage girl — played in an astonishing breakout performance by newcomer Adèle Exarchopoulos — “Blue Is the Warmest Color” at first seems like nothing new: Portraying the day-to-day life of Exarchopoulos’s character, also named Adèle, Kechiche hews to the time-honored French tradition of dressed-down, realistic staging and style, devoting long, seemingly spontaneous sequences set at Adele’s high school and at home with her working-class parents.

Those unforced, quotidien rhythms don’t perceptibly change once Adele meets Emma (Léa Seydoux), a fresh-faced, blue-haired art student she first glimpses on a crowded street, then pursues into a lesbian night club. The two women fall into a rapturous, physically electric affair, with Adèle at first bewildered and finally beguiled by Emma’s assured delivery of a sentimental education.

The high point of that tutorial is the prolonged, intimate sex scene that this year made “Blue Is the Warmest Color” the talk of Cannes, where it won the festival’s top awards (shared by the director and his two fearless leading ladies). Debate immediately ensued around whether Kechiche was perpetuating an exploitative heterosexual male gaze or claiming new space for representing gay desire on screen. Reasonable people can disagree, but what sets “Blue Is the Warmest Color” apart from sensationalism or pulp are the daily moments that precede and follow the more notorious sex sequence — the myriad otherwise forgotten occurrences that comprise a love affair that, when it inevitably ends, turn out to have been the most important all along.

Loosely based on a graphic novel by Julie Maroh, “Blue Is the Warmest Color” follows Adèle over the course of a decade, in which time she becomes a teacher and settles into domestic housekeeping with Emma, whose bohemian social circle is a quiet and an uncomfortable fit. As much press as that sex scene has received, far more eloquent is another protracted sequence in which Adèle, who has knocked herself out cooking for a dinner party, becomes increasingly marginalized among Emma’s far more sophisticated friends.

Viewers may initially wonder about the scenes Kechiche chooses to focus on: dinners with each young woman’s family, for example, don’t seem to “go anywhere” in the conventional sense of the term. But what he and his actresses build in the course of three hours is a vivid, even tactile sense of the classes and cultures each of them inhabits, and that ultimately may prove their undoing.

Not since Kenneth Lonergan’s “Margaret” has a filmmaker been so willing to stick with a young female heroine and see her through to the end — or, in the case of Adèle, at least one end. Exarchopoulos is so convincing as a young woman in the throes of longing, love, lust and devastating rejection that, in the film’s shattering final sequences, filmgoers will sense that they’re not watching a movie as much as witnessing the most private moments of someone’s life, from its headiest highs to its most crushing, depressive lows.

Hours, even days later, they may find themselves thinking of Adèle and wondering how she’s doing — only then realizing how completely this fictional but very real creation has winnowed her way into their hearts and minds. That’s great acting. It’s great art. And that’s why “Blue Is the Warmest Color” is a great movie.

★ ★ ★ ★

NC-17. At area theaters. Contains explicit sexual content. In French with subtitles. 179 minutes.