In a bit of braggadocio that would make the many hairs on Don King’s neck stand up, Cinderella Man opens with a quotation from Damon Runyon. In it, Runyon calls Jim Braddock’s human-interest story incomparable to any other in all boxing lore.

That lofty-standard epigraph seems like pre-fight baiting from director Ron Howard, producer Brian Grazer and co-screenwriter Akiva Goldsman — Oscar winners all for A Beautiful Mind.

Only brief bits of hot, steaming hokum creep into the film, which is both a second-chance fairytale about pugilism’s mythical pull and a stark look at the grimy reality of Depression-era life. It’s anchored by yet another captivating chameleon turn from Russell Crowe, his entire body transformed into middle-heavyweight shape.

Far and Away, Howard’s last attempt to connect boxing and the American dream, was a vanity-project mess that focused too exclusively on stars Tom Cruise and Nicole Kidman. Here, he wisely doesn’t use the Braddock family as a microcosm of the Depression. Economic struggles of the day extend all the way to the gasman turning off their heat. They’re big-picture moments masquerading as minor details, and they help ground the film.

The story opens in 1928, as Braddock (Crowe) is the king of New York’s middle-heavyweight bracket. After each $8,000 bout, three kids and a loving wife, Mae (Renee Zellweger), await him at a New Jersey home, and he’s got “gold for the grandkids” invested in a taxi company.

Plus, he’s got at-cha-cha-cha trainer Joe Gould (Paul Giamatti) in his corner to keep him in fine shape. As one promoter tells Gould, “They oughta put your mouth in a circus.” An atypically clean-shaven Giamatti turns in a sweaty, aggressive motor-mouth performance that has the make-up Oscar for Sideways, or at least the nomination, written all over it.

When Black Monday hits Gould, the Braddocks, everybody, it’s shown in a fine transitional camera pan. The Braddocks’ well-lit dresser-top luxuries fade away into the dim basement flat they’re forced to move into.

Chemistry between Crowe and Zellweger is fine, but it’s more tender and real with their onscreen kids. The everyday ways in which they try to retain breadwinner dignity — and shield the scope of their poverty from the children — are heartbreaking, as is Crowe’s breakdown while seeking a hand-up in an ivory tower of boxing-promoter bigwigs.

Before long, Braddock has become a charity-case fighter (taking on nobodies with his broken hand for pitiful payouts) and a low-wage dockworker on the days he can get it. But then Gould comes calling with a $250 payday to fight the No. 2 title contender in a no-consequence contest. Crowe’s scan of the crowd before the fight shows the tank on Braddock’s resolve filling up on the way to an unexpected win.

Thus begins Braddock’s yearlong climb back to prizefights, culminating in a blow-by-blow with Max Baer (Craig Bierko), a flamboyant playboy known to pack a fatal, brain-dislodging right hook.

Even though Bierko’s empty-slate stare is frightening, Cinderella Man sloughs a bit when it turns Baer into some sort of fearsome monster Braddock will have to face.

But it does allows Zellweger to make the most of her role; she goes from the cornpone yelping of Cold Mountain to the more subtle routine of preparing for life as a widow. And cinematographer Salvatore Totino allows the audience to feel the smoky fervor, brutality and tension in each round of the epic Baer-Braddock bout.

The only bit of silly hyperbole comes when the crowd of 35,000 gathered to watch it hushes to a pin-drop silence as Braddock approaches the ring. Low, rumbling chatter, maybe. But the air wouldn’t be empty of cheers.

Auditoriums might not be either for this tremendously entertaining movie that doesn’t just pay lip service to the idea of a boxer chasing a ring dream that no one sees but him.