The Wrestler, Darren Aronofsky, 109 mins, 15

Mickey Rourke's moving portrayal of a failed fighter shows he should never be counted out

'I'm an old broken-down piece of meat," laments the hero of The Wrestler. Broken-down he may be, but he's still meat – living flesh – rather than a conglomeration of pixels, and that's something in today's American cinema.

We've become so used to CGI "adjusting" actors' faces and bodies – from invisible tucks to full Hulk-style mutation – that we've forgotten how poetic it can be when an actor lets himself be viewed as unashamedly gone to seed. The sheer weight of flesh is the subject of Darren Aronofsky's low-budget realist drama: the film is about the struggles of a failed wrestler, but it's also about the lumbering man-mountain that the film's star has become and, indirectly, about the wear and tear, the workouts and the bruisings, that have made Mickey Rourke what he is now.

The protagonist is Randy "the Ram" Robinson – a star wrestler in the 1980s, now grinding away at the bottom of the US fight circuit, but dreaming of his comeback. Rourke too was a golden boy of the 1980s, but dramatically lost his way, and his looks, in his misguided determination to be a boxer. Rourke hasn't been entirely absent from the screen, but it's true to say that his tender, self-revealing performance here represents a magnificent comeback.

Randy the Ram is someone who not just coulda been a contender, but was one – who even became a character in a Nintendo game and had his own action-figure toy. We don't learn what went wrong in Randy's life, but he's now penniless and living in a trailer park, estranged from his grown-up daughter (Evan Rachel Wood). Apparently Randy didn't hang up his glittery leotard when he should have done, pursuing his myth beyond its expiry date: he clings desperately to the living effigy he's created, the bulked-up titan with rubberised muscles and peroxide Viking locks.

The Ram embarks on a tentative romance with lap dancer Cassidy, played by an affectingly no-nonsense Marisa Tomei. Randy thinks she cares for him, and perhaps she does, but she understands the reality-fantasy divide: she knows they're in the same trade, using their bodies to play a part, only she's able to stop when she gets home.

With its spare, unsentimental script by Robert D Siegel, the film is very much about demystification. It demonstrates all that's faked in the wrestling world, from Randy's persona to the moves themselves: backstage before a match, a roomful of affable goliaths quietly plan their strategy, the only rule being that the good guys, or "faces", must triumph over the gurning thugs, the "heels".

Yet within this play-acting is a high degree of corporeal reality. That's real muscle going into that ring, real body weight crashing to the floor, real blood spilled, even when it's done theatrically: Randy may fake his injuries for showbiz's sake, but it still takes a razor to the forehead. Wrestling's grimmest theatre is a bloodthirsty institution called CZW, "Combat Zone Wrestling", involving household tools, barbed wire and such ruthless opponents as the (real-life) "Necro Butcher", who starts the show by stapling a banknote to his forehead before producing a kitchen fork to make a meal of Randy.

The fight scenes in The Wrestler – staged in school gyms or grime-encrusted pool halls – are brutal, squalid and matter-of-fact, worlds away from the grand opera of Raging Bull. The Wrestler also recalls 2006's The Singer, in which Gérard Depardieu, as an ageing crooner, similarly played on his own history, rising with dignity above his supposed ruin. Depardieu's key line – "You're only corny because you've lasted" – applies just as well to the Ram here, and to Rourke, whose somewhat childlike tenderness is still visible through the leather-lipped mask that his face has become.

Rourke gives a wholehearted, defences-down performance, from the bouts to Randy's most unglamorous moments, not least when jabbing steroids into his perma-tanned arse. For the first time in ages, the star has a chance to show vulnerability and humour: a superb scene, apparently improvised, has the Ram reluctantly serving on a deli counter, and rising to the task with winning showmanship and charm.

The Wrestler is also a comeback for director Aronofsky, whose last film was the metaphysically overblown The Fountain. Here Aronofsky pares down his style, inspired (I'd guess) by the hard-tack realism of Belgium's Dardenne brothers: you see it in the way that the hand-held camera often hangs on Rourke's shoulders, and in the pitilessly drab settings, Aronofsky claiming New Jersey as a Belgium of his own.

The Wrestler is uneven – the scenes with Randy's daughter don't quite take off – but it's insightful, affecting and bracingly free of bullshit. The Ram may get to deliver his big "I'm still here" speech at the end, but we're left guessing whether it truly signifies triumph or more desperate self-delusion. The final shot, depicting Randy's literal and symbolic leap into the void, is a classically teasing open ending. But The Wrestler shows Aronofsky leaping into the void too, and his nerve pays off gloriously.