If there were ever any doubt that Russell Crowe is the greatest screen actor of his generation, "Cinderella Man" should put matters to rest.

Equal parts "Seabiscuit" and "Rocky," Ron Howard's film finds Crowe playing real-life heavyweight fighter James Braddock. It's not a flashy role - Braddock was a quiet, even-tempered and modest man devoted to his wife and kids. No chest-thumping or womanizing for this guy.

Which makes Crowe's performance all the more remarkable. Denied the sort of character hooks that make for fine scenery chewing, Crowe has been forced to go deep within himself, calling on his own reserves of decency and inner strength. The resulting performance is inspiring, heart-breaking and overwhelming in its simple eloquence.

Cliff Hollingsworth's screenplay begins in the late 1920 s with Braddock winning a major bout in New York City. He returns to his pleasant home in suburban New Jersey, his wife, Mae (Renee Zellweger), and their three children. The camera pans across Jim and Mae's well-appointed bedroom, taking in the personal objects and framed photos atop a dresser.

And then, in a transition that covers five years and one of the greatest upheavals in American history, the scene changes to a moldy cellar wall, crude wooden shelves, a bare light bulb. It's now 1933, and Jim Braddock has been wiped out by the double whammy of a failed boxing career and the stock market crash.

Jim, Mae and the kids are renting a bleak basement apartment. It's winter. Jim can only occasionally find work on the docks. Dinner is a slice of fried bologna and a cup of watered-down milk. If something doesn't happen soon, they're going to have to ship the children off to live with relatives.

We share Jim's shame at standing in line for a few dollars in relief money. Even more dispiriting is a trip to Manhattan so that he can pass the hat among the boxing managers and promoters for whom he once earned a small fortune.

Finally he's so desperate that despite near-starvation and a broken hand he begs his old manager (Paul Giamatti) for a chance to fight in an undercard in a local ring. His performance is so miserable that he's banned from boxing.Amazingly enough, within a couple of years Braddock was fighting to take the crown away from Max Baer, a testosterone-fueled brute who already had killed two opponents in the ring.But by this time Braddock's comeback story, his personal integrity (with his first winnings he returned to the welfare office and paid back the state) and his family image had made him a symbol of hope for a dispirited nation. The press dubbed him the "Cinderella Man."The film's last half-hour is devoted to a blow-by-blow re-creation of the Braddock-Baer fight, and it's one of the most grueling, exciting and tense boxing sequences ever captured on film. Special kudos to Craig Bierko, whose Baer is a scary blend of unsuppressed ego and physical intimidation. Even if you know how the fight's going to turn out, you'll be wrapped up in the suspense of this monumental slugfest.Howard steers away from directorial flourishes and attention-grabbing visuals. Usually he approaches his story with a handheld camera whose occasionally jumpy images suggest the Braddocks' struggle for survival and the bumpy road of Jim's comeback.Although Crowe's work here may be the most convincing display of pure star power we'll see this year, one cannot discount the contributions of the supporting cast.Zellweger's Mae is more than just the supportive little woman - she's an iron-willed realist who knows when she can change her husband's mind and when she can't. And the film carries a refreshingly strong suggestion of eroticism within marriage - usually in a Hollywood movie, romance ends with the wedding ceremony.Giamatti is his usual excellent self as Braddock's trainer/manager, finding a forcefulness that's a 180-degree turn from his work in "Sideways.""Cinderella Man" isn't a yarn with a lot of hidden meanings. It is what it is: a great story of a guy who fought back from obscurity and exhibited a champion's heart.