For film fans, Bill Murray has long been something of a saint.

It's not for his good works, but for being his own man, a good egg whose approachability belies his stardom and, of course, a brilliant comedian.

Ghostbusters, Groundhog Day and half a dozen films with Wes Anderson put him in the top bracket of beloved screen actors.

There is another side to Murray's character: his willingness to take a punt on young directors.

Anderson and Sofia Coppola are the best examples, Murray's presence in Anderson's Rushmore and Coppola's Lost In Translation (in which he also demonstrated his dramatic chops) was crucial to the tone each director was trying to establish, steering each away from whimsy.

Murray performs this service again, with the gorgeous comedy St Vincent. First-time writer-director Ted Melfi clearly has talent: his story about the friendship between a 12-year-old boy, all at sea when he moves to Brooklyn with his single mum, and their curmudgeonly neighbour, is scripted with rare warmth, and directed with a sure eye for the details of character and milieu.

But it wouldn't be the same film without Murray, whose rejection of sentimentality, willingness not to be liked and nonchalant delivery of a punchline clears the way for the audience to laugh out loud and tear up.

Murray is grizzled, boozing, offensive Vincent, who lives alone with Felix, a cat whose unbelievable bad looks belong in a cartoon.

Retired, he divides his time between the bar, the racetrack and Daka (Naomi Watts), a pregnant Russian pole dancer and prostitute, who he will describe to the boy as "a lady who works at night".

Deep in debt, Vincent spies some extra cash when Maggie (Melissa McCarthy) moves in next door and needs someone to look after her son Oliver (Jaeden Lieberher) after school.

Not only does he get babysitting fees, but it turns out that the boy is a natural when it comes to betting - the track being just one of Vincent's natural habitats to which the child is introduced.

The character arcs aren't particularly original. We'll eventually learn that Vincent has a good heart, with elements to his life story that mitigate his grouchiness; the boy is a frail and easy target for school bullies, until his new minder teaches him some moves, and grows under his tutelage; Maggie is a typical, put-upon, hardworking mother, Daka the broader comic presence.

But Melfi and all of his cast bring huge nuance to these outlines.

In an atypically straight role, McCarthy is touching as the mum who has salt rubbed into her wounds when her philandering ex files for custody of their child.

Conversely, Watts, who we're much more accustomed to seeing in drama, is a comic revelation as the no-nonsense Daka, not least when attempting to pole dance while heavily pregnant.

And Chris O'Dowd chips in with customary charm, as the boy's Catholic school teacher, who informs his class that "dumbness will not play well in heaven".

Throughout, Murray and young Lieberher strike up a lovely rapport, each subtly delineating the progress from indifference, through curiosity to affection.

Around them, Melfi adds numerous terrific touches, such as Vincent's vintage car, which looks as though it's made entirely of wood, and the skinflint's memorable idea of sushi.

All of this assist Murray in constructing one of his richest characters. In many ways Melfi reminds me of Wes Anderson, without the baroque embellishments in the storytelling.

And like Anderson, he's found St Bill.