He may manage to turn an earthy flower girl into the very model of a proper lady, but it’s clear in the Old Globe Theatre’s “Pygmalion” that Professor Henry Higgins is fated to remain an overgrown boy.

That’s the charm and the sorrow at the center of Nicholas Martin’s savvy, sumptuous and very funny production, which does the George Bernard Shaw masterwork proud.

And it finds its expression in the youthful good looks and gleefully heedless comportment of Robert Sean Leonard as Higgins, the expert in “the science of speech” who wagers to make the street peddler Eliza Doolittle (Charlotte Parry) fit for high society.

His Higgins makes a great show of not being ruffled by much (at least until Eliza starts taking control of the game). And yet as the pompous prof admits to his own mother in a moment of offhand candor, “I’ve never been able to feel really grown-up and tremendous, like other chaps.”

No wonder: Mrs. Higgins (played with an exquisite sense of the imperious by Kandis Chappell) could cut diamonds with her withering asides, and she seems to try and engineer her son’s behavior as doggedly (if more subtly) as Henry “trains” Eliza.

When Henry remarks to Mom that “my idea of a loveable woman is something as like you as possible,” we half-expect Freud to leap down from the chandelier that dangles over designer Alexander Dodge’s stately, deliciously detailed drawing room.

Still, it’s strange at first to see Leonard – the Tony-winning stage and screen star who first made a splash as a fresh-faced lit student in “Dead Poets Society” – stepping into Henry’s shoes. Rex Harrison, who famously played the role in the enduring musical adaptation “My Fair Lady,” was in his 50s in the film version and his 70s for a 1981 Broadway revival. (Leonard is 43.)

Yet Leonard and director Martin (who was just named the Globe’s newest associate artist) make sense of this Higgins as a kind of overeducated man-child who fusses when he can’t have his way.

And our Ms. Doolittle makes sure of that. The British-born Parry traces Eliza’s arc beautifully, from proud but churlish girl who immodestly excavates her nose with Henry’s handkerchief in an early scene, to a robotically (and comically) proper gentlewoman treading delicately in posh clothes a bit later.

That one’s an indelible scene: Eliza perching with cocked head, like a parrot or the sweet-singing mechanical bird in the fable “The Nightingale,” while the others talk to her in slow, deliberate cadences, as if seeking clues from a Magic 8 Ball.

Higgins’ jolly misogyny (an aspect that can make this 100-year-old play tricky to stage, in the manner of Shakespeare’s “The Taming of the Shrew”) is tempered by the more gracious ways of his fellow linguist and new best pal Col. Pickering, played with understated wit and dignity by the ageless Paxton Whitehead.

And while “dignity” is likely the last word one would attach to Mr. Doolittle, Eliza’s ethically flexible father, his portrayal by longtime Globe hand Don Sparks brings the mightiest laughs. Suffice to say that, to use Mr. Doolittle’s own term, this shambling genius of a wheedler has ginger to spare.

The show also boasts piquant performances from Deborah Taylor as the fruitlessly scolding housekeeper Mrs. Pearce, Danielle O’Farrell (a standout member of the Globe/USD acting ensemble) and Maggie Carney as high-society hangers-on, and Robbie Simpson as Eliza’s foppish suitor Freddy.

Mark Bennett contributes suitably elegant music, and Philip S. Rosenberg’s luxuriant lighting helps Robert Morgan’s costumes (some of them making encores from a long-ago Globe “Pygmalion” pop.

The one glitch on opening night (besides Leonard’s sometimes casual English accent) involved a balky turntable that left Whitehead stuck only partway onstage. In a bit of Shavian serendipity, though, subsequent lines straight from the script came off to the audience as actorly improv – particulary Henry’s, “Well, I think that’s the whole show.”

A production where the rough patches are transformed into triumphs? That’s Higgins (and Shaw) all the way.