Billy (Jake Gyllenhaal) doesn’t stand by his manager (50 Cent) after tragedy strikes. (Scott Garfield/The Weinstein Company)

Jake Gyllenhaal undergoes yet another startling physical transformation in “Southpaw,” a by-the-numbers boxing picture that benefits considerably from its star’s tenacious, fiercely obvious commitment. No one will accuse Gyllenhaal of phoning it in on “Southpaw,” in which he plays a down-on-his-luck fighter struggling to make his big comeback. He grunts and punches and scratches and glares it in, bleeding copiously in set pieces that thud and splatter with woozy, percussively potent verisimilitude.

Put more simply, there’s a lot of punching in “Southpaw,” which combines the training narrative from “Rocky,” the visceral ringside energy of “Raging Bull” and the rank melodrama of “Million Dollar Baby” to make something, if not new, then at least stylish in its derivativeness. Gyllenhaal plays Billy Hope, once an orphan in Hell’s Kitchen, now the light heavyweight champion of the world, living in nouveau-riche splendor with his wife, Maureen (Rachel McAdams), and their cute, down-to-earth daughter, Leila (Oona Laurence). “Southpaw” is not a rags-to-riches story: Billy is already on top of the world when the movie opens, lavishing his entourage with Cartier swag and contemplating a $30 million contract with HBO.

When the reigning junior middleweight boxing champion (Jake Gyllenhaal) is struck by a horrific tragedy a domino affect causes him to lose his daughter, manager and home. Now he has to work to get all that he loves back with the help of a new trainer. (Weinstein Co.)

That all changes when tragedy ensues and Billy is forced to overcome grief, avenge his personal loss, rescue his career and put his family back together. It should surprise no one that this endeavor entails trading his flashy manager Jordan Mains, played with understated elan by 50 Cent, for Tick Wills, a quiet corner man from a scruffy neighborhood gym. A font of shamanic wisdom — delivered by way of Forest Whitaker’s brooding, iconic whisper — he joins a long line of such magical helpmeets, from Morgan Freeman’s Scrap-Iron Dupris to Will Smith’s Bagger Vance.

Filmed with a de-saturated palette and painfully graphic close-ups by Antoine Fuqua, “Southpaw” plays like a musical in which the performance numbers are its fights, a pageant of beat-downs, bloodlettings and bodies plummeting to the canvas like so many felled sequoias. Gyllenhaal proves himself a compelling, even mesmerizing presence amidst the action, even at its most hyperbolic and cliched. In last year’s “Nightcrawler,” he was alarmingly emaciated and wild-eyed, giving off a mangy, half-feral vibe. Here, he’s beefed up, impressively cut and prodigiously tattooed, his face reduced to a barely recognizable pulp of scrapes, lacerations, bulges and bruises.

When “Southpaw” switches tracks from revenge narrative to redemption tale, Gyllenhaal doesn’t skip a beat. He even makes the de rigueur makeover montage — shots of him tossing around the ol’ medicine ball and hitting a truck tire with a sledgehammer — less banal and more convincing than it deserves to be. “Southpaw” may be rote, predictable and mawkish, but none of those faults lie in its star. Even when he looks like an unholy mess, he transcends the movie he’s in.

R. At area theaters. Contains violence and obscenity.
123 minutes.