A modern-day Scrooge is moved by the plight of a young boy in Theodore Melfi's touching and frequently uproarious comedy.

There are neither jingling bells nor ghostly visitations in St Vincent - the only spirits are swigged from a bottle - but Dickens' underlying theme of the redemption of the human spirit rings true in this valentine to Bill Murray.

The Oscar-nominated star of Ghostbusters, Groundhog Day and Lost In Translation is in riotous form in Melfi's delightful film, deploying split-second comic timing to devastating effect as he reveals a beating heart of gold beneath the shambolic appearance of his penny-pinching curmudgeon.

His irascible old coot might gamble, smoke and drink to excess, and seek physical pleasure in the company of a heavily pregnant Russian prostitute, but we fall head over heels for Murray's virtuoso portrayal and it's a love affair that endures the film's occasional lull or sloppy characterisation.

Newcomer Jaeden Lieberher is magnificent as the spirited tyke, whose innocence and unwavering faith provide a beacon of hope for the self-destructive codger to stumble back into the land of the living.

Writer-director Melfi wrings us dry of laughter and tears in the process.

Vincent (Murray) lives in a ramshackle house in Brooklyn with a pet cat and dreams of the past.

He owes a small fortune to bookie Zucko (Terrence Howard), who is reluctantly threatening to smash Vincent's kneecaps unless fortunes change.

Lady Luck smiles on the sexagenarian loner when struggling single mother Maggie (Melissa McCarthy) and her son Oliver (Lieberher) move in next door and Vincent exploits Maggie to become the lad's babysitter.

"He's sort of cool, in a grouchy sort of way," Oliver assures his mother about his new guardian.

While Maggie works long hours to keep a roof over their head, Vincent introduces Oliver to horse racing, his feisty Russian companion-for-money Daka (Naomi Watts) and an elderly woman with Alzheimer's called Sandy (Donna Mitchell), who he visits at an expensive nursing home.

When Vincent's schoolteacher Brother Geraghty (Chris O'Dowd) asks his impressionable charges to deliver a verbal report on someone they consider a 21st-century saint, Oliver knows exactly who he wants to canonise.

St Vincent is anchored by Murray's award-worthy performance, but supporting cast is equally impressive, often in underwritten roles.

McCarthy abandons her usual schtick to embody a mother in crisis and Watts plies a thick cod-eastern European accent as the working girl looking for a break.

O'Dowd scene-steals with aplomb as a holy man with heavenly quips: "I'm a Catholic, which is the best religion because we have the most rules."

Aided by a leading man in rude health, writer-director Melfi doesn't slather on the sentimentality too thick as he exposes glimmers of hope for each dysfunctional character and encourages them to walk towards the light comedy.