Bill Murray finds the perfect Bill Murray role in “St. Vincent.” The veteran comic and sometimes dramatic actor nails the movie’s title role of grouchy Brooklyn retiree Vincent McKenna.

Murray’s Vincent amuses and charms, despite the character’s apparent lack of interest in pleasing anyone other than himself. At 64, Murray is ripe for the part, comfortable and authentic playing a character his own age. He does so without a trace of actor’s vanity.

Murray has won many acting awards, most of them for his performances in Sofia Coppola’s “Lost in Translation” and Wes Anderson’s “Rushmore.” He’s never received filmdom’s biggest prize, the Oscar. “St. Vincent” may change that. But the movie being so obviously a showcase for Murray may work against him. The charge of being Oscar bait, however, needn’t stop non-Academy of Motion Picture Arts and Sciences members from rolling with “St. Vincent.”

Murray co-stars with Melissa McCarthy, a movie star whose comic roles usually steal the show. She shifts gears in “St. Vincent.” McCarthy plays a suddenly single mom struggling to pay the rent and raise her 12-year-old son. She’s mostly a straightwoman to Murray’s grumpy old man. McCarthy hits Maggie’s dramatic notes solidly and also gets one of the film’s bigger laughs.

Maggie moves into the small Brooklyn house next to Vincent’s likewise small, working-class home. When her work as a nurse keeps her at the hospital for hours longer than she anticipated, she recruits Vincent to watch her son, Oliver. Maggie knows her ill-tempered old neighbor isn’t the ideal guardian for Oliver, but options are limited, time is short.

On the surface, at least, Vincent isn’t doing Maggie, or Oliver, any favors. He charges the financially stressed mother by the hour.

Despite his duties to care for Oliver, Vincent doesn’t alter his behavior or routine. He takes innocent, polite Oliver to such regular stops as the bar and the horse track. Nor does Vincent stop seeing Daka, a pregnant stripper who, as Vincent euphemistically tells Oliver, is a lady of the night.

Naomi Watts’ co-stars as Daka, speaking the role with a cartoony Russian accent, playing it in wide comic strokes. Russians are Hollywood’s current ethnicity of choice for bad guys and questionable characters. Watts, of course, is among contemporary cinema’s finest actresses. Her deeper skills go untapped as Daka. She’s playing, and flashing, to the gallery.

Jaeden Lieberher co-stars as Oliver. The “St. Vincent” team struck gold with Lieberher, a Philadelphia native who’s graduated from Hot Wheels, Google and Hyundai commercials to “St. Vincent,” his second film. A natural on screen, Lieberher and Murray’s easy rapport ensure that the movie’s boy and old man friendship becomes the film’s warmly glowing soul.

It’s probably best not to think too deeply about “St. Vincent’s” plot developments. Or dwell on the false, feel-good way the story wraps up. “St. Vincent” gets much more right than it gets wrong.

The feature film debut from TV commercial director Ted Melfi, “St. Vincent” is most of all the province of Bill Murray.

Watching him work in this quintessential Murray role is the the best reason for the movie to exist.