A film like A Star Is Born has one of the most ambitious tasks in Hollywood: to convince the audience that its fictional musical megastars really could be megastars in our world. It’s not enough to have the charisma-wattage of Bradley Cooper and Lady Gaga – you need the songs as well.

An example: the otherwise enjoyable TV series Empire was kept firmly in soap territory by the ersatz swag of its middling, specially penned rap tracks. Or the Hugh Grant-Drew Barrymore romcom Music and Lyrics, whose tunes, while strongly written, were pastiches put to work as cute plot devices rather than songs in their own right.

A Star Is Born needs to be more than that. As a serious drama about addiction, and the supernatural, transformative, sometimes erotic power of music, it needs songs that are earnest and instantly classic. Against the odds, it succeeds.

The soundtrack moves chronologically through the story, including snatches of dialogue to jog the memory (or generate light spoilers). It begins with Black Eyes, a swaggering rock’n’roll song performed by Cooper’s country rocker Jackson Maine, which ladles up big dollops of The Seeker by the Who with a drizzling of Lynyrd Skynrd and My Morning Jacket. The guitar shredding, meanwhile, is like Neil Young without the ragged edges – unsurprising perhaps given that a major creative force here is Lukas Nelson (son of Willie) whose band Promise of the Real currently back Young. Nelson has numerous co-writing credits across the soundtrack, alongside Gaga, Cooper, Mark Ronson, Jason Isbell and Diane Warren.

Cooper makes you sick, really. He delivers a very accomplished lead performance in the film and, as director, crafts scenes of intimate naturalism and big-guns emotion with equal aplomb. His arguably unnecessary shirtlessness in one scene was instantly validated by the audible ripple of arousal around the cinema I saw it in. And to top it all, he can sing: convincingly snarly on blues-rockers like Alibi, stoic on the extremely strong Isbell-penned country ballad Maybe It’s Time, affectingly doleful on his duets with Gaga.

His Jackson is an alcoholic who meets Ally, a waitress and jobbing singer who entrances him in a bar with a performance of La Vie en Rose. It’s a nice opening performance from Gaga: the low-key setting hardens any potential ripeness, and perhaps only she could create its balance of genuine melodrama and knowing camp. Ally turns out to be an instinctive songwriter, and briefly knocks Jackson out of his stupor; the pair fall in love. Her star is indeed born, but Jackson struggles to stay in her slipstream, buffeted by his drinking, familial pain, tinnitus and perhaps a bit of jealousy.

Cover art for the A Star is Born soundtrack. Photograph: AP

The film’s most powerful sequence sees the two in perfect equilibrium. Jackson invites Ally out at an open-air concert to perform Shallow, the song they worked up together the previous day. Their performance is pure symbiosis, him needing her stability and creative energy, she needing his big stage, and Gaga is extraordinarily good. Moments before she makes the octave jump for the big chorus, her face flickers with terror, then as she is singing it, disbelief – a moment that announces music is bigger than its performers, that it plays them rather than the other way round. The song itself is torrid yet robust, and truly outstanding.

As her solo career takes off, Ally segues from Jackson’s earthy songcraft towards poppier territory, via another highlight: Look What I Found, a joyous bit of Aloe Blacc-style neo-Stax soul that suits Gaga incredibly well. It was at this point of the film, with Jackson voicing scepticism towards her glossy new sound, that I pre-emptively cringed. It looked like we were heading for a retread of La La Land, where pop is snootily compared with the “real”, “authentic” stuff played on wooden instruments without choreography. But this is where the casting of Gaga delivers an extra level of legitimacy. The commitment and skill she brings to these performances shows that pop is just as worthy, and allows Ally to exacerbate Jackson’s creative frustration even if she doesn’t mean to. When she berates Jackson for his condescension, it is a moment of bracing anti-snobbery.

Nevertheless, it needs that authority from Gaga to lift some slightly underwritten material in this section, as she shows off another lesser-heard side of her real-life work: the R&B minimalist. Heal Me has lovely, dreamy verses, but Hair Body Face is a definite third single, and the opening to Why Did You Do That? is perhaps a bit heavy-handed: “Why do you look so good in those jeans? / Why do you come around me with an ass like that?” is a motorway-legal signpost to point out the increasing creative differences between the central pair.

The piano ballads, though, are truly blue-chip. I Don’t Know What Love Is is a beautiful duet, Cooper giving a modest extra grain to Gaga’s vibrato, and it is followed by Is That Alright?, whose earnestness is again completely sold by Gaga. “I want you to look right in my eyes / to tell me you love me / to be by my side / I want you at the end of my life / I want to see your face / When I fall with grace / At the moment I die” – on the page it is almost ludicrous, but on record it grabs your ribcage. Your least ironic friends will choose this as their wedding dance music, and it’ll work. These songs feel like they’ve been in the songbooks of Elton John or Adele for years, and they enable A Star Is Born to succeed in that task of making us believe in these megastars.

The soundtrack, like the film, ends with a song whose title I don’t even want to print lest it give a sense of the ending. But suffice to say it is another hyper-emotional piano ballad, where Gaga channels Whitney for the verses but does something much more affectingly girlish and vulnerable with the high-pitched chorus.

Cooper sketches out his rockstar in admirably fine lines: boozy, bluesy and with a tot of self-loathing that all comes through in his singing. But it is Gaga who is the true star: a woman capable of every kind of pop, who shows how it can all throw your life into the sharpest relief.