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There are movies that are great as cinema: examples of visual storytelling at its purest, most inventive and emotionally expressive.

Then there are movies that are great simply as containers for a performance: reminders that, for all the structural, technical and aesthetic elements that come into play in a film, it’s the stars we come to see.

“Judy” is just such a sturdy, dependable vehicle which, in this case, carries the precious cargo of Renée Zellweger in a dazzling portrayal of Judy Garland at the end of her life. Tough, vulnerable, resilient and wrecked, Zellweger’s Garland both leans into the myth — she even wears her “What Becomes a Legend Most?” mink in some sequences — and slyly subverts it, with moments of self-aware humor. Zellweger doesn’t deliver an impersonation of Judy Garland as much as an interpretation, adjusting her own vocal register but never to the point of erasure or mimicry. The result is a relatively straightforward slice-of-life biopic, bogged down with flashbacks and backstage histrionics, that nonetheless offers an utterly transfixing glimpse at the art of screen performance writ gloriously, glamorously large.

“Judy,” which has been adapted by screenwriter Tom Edge from the play “End of the Rainbow,” chronicles Garland’s you-had-to-be-there engagement at London’s Talk of the Town nightclub, where for five weeks in 1969 audiences were on the edge of their seats, either in rapturous attention to her songs or wondering if she’d make it onstage at all. As the film opens, we’re made privy to the reasons Garland took the gig: Broke, unemployable and uninsurable, she’s forced to leave her two children with ex-husband Sid Luft (Rufus Sewell) while she tries to build a more stable home life. Deeply in debt to back taxes, she reluctantly agrees to leave the country for England, where she can make a stab at refilling the coffers.

Actually, the film opens even earlier in Garland’s life, when as a young girl (played by Darci Shaw), she’s being scolded by MGM chief Louis B. Mayer for being disloyal and ungrateful. Throughout “Judy,” director Rupert Goold leaps back to the time when the “fat-ankled, snag-toothed” Frances Gumm is being groomed to become a bankable child star, whether through the cruel manipulations of Mayer or the pill-pushing ambitions of her martinet of a stage mother. “There’s the cake. Don’t eat it,” Mrs. Gumm barks at a fake 16th birthday party thrown for her daughter, words that come back to the middle-aged Garland later in the film with pointed poignancy. By the time Zellweger’s character makes her grand London entrance, she’s addicted to pills and alcohol, a chronic insomniac and bedeviled by paralyzing self-doubt and stage fright. And we understand why.

The Garland of “Judy” is so fragile, so physically and mentally ruined that it’s all the more breathtaking when she proves she’s still got it. Zellweger’s opening nightclub number, “By Myself,” is an absolute barnburner, a fabulous performance-within-a-peformance that not only captures Garland’s belting power, but her slightly glazed nervous energy and darting physical tics. Zellweger bears zero resemblance to Garland in real life — contact lenses and wigs help, along with the familiar cigarette pants and embroidered cocktail ensembles — and her soft, high speaking voice is missing that distinctive, throaty sob. But when she takes the stage, whether at the top of her game or dissolving into a puddle of insecurities and defeat, she owns the role from the pipes right down to the gams.

The night-of-show numbers in “Judy” are magnificent, with Zellweger more than holding her own on ripping renditions of “For Once in My Life” and “Come Rain or Come Shine.” But it’s the quieter moments — an impromptu performance of “Get Happy” at the apartment of a gay couple she befriends, a deeply moving version of “Over the Rainbow” — that give “Judy” its dimension and depth. Going beyond predictable tragic-diva tropes, Zellweger invests Garland with her own ferocity and focus, to the point where the technical commitment and strenuous physicality of the performance becomes one with the character’s own extraordinary grit and courage. Playing Garland’s soft, unprotected center as well as her sharp corners — “Judy Garland, born in a trunk,” she says gamely at one point — Zellweger isn’t delivering an homage to a worshiped icon, but to old-school Hollywood professionalism.

The ugly underside of that professionalism — the sheer will it takes to get through the number — becomes the most recognizable motif in “Judy,” in which a teenage Garland has had her instincts so thoroughly destroyed that she asks Mickey Rooney if they’re dating “so I’ll know how to look at you.” The love flowing over the footlights might be addictive, but it comes at an unfathomable cost, twin realities that Zellweger expresses with subtlety and skill. It’s a coincidence that “Judy” takes place in 1969, which is also the same time period of Quentin Tarantino’s “Once Upon a Time in Hollywood.” And like Tarantino’s film, this one seeks to honor the largely invisible labor and self-denial beneath the high gloss of celebrity. “I think maybe I was just hungry this whole time,” Zellweger’s Garland says wryly. It’s a throwaway line, but one that gets to the starving heart of a gifted artist who dared to dream of having her cake, and eating it too.

PG-13. At area theaters. Contains substance abuse, mature thematic elements, some strong language and smoking. 118 minutes.