Have you heard about this new comedy to hit Broadway? About the Manhattan swell and the farmer’s daughter who team up to swindle some locals (aided by her wily old cuss of a father), guzzle some bourbon, and spoon a little under the autumn moon? By this Eugene O’Neill fellow?

Hang on. O’Neill’s famously bleak oeuvre is known for including exactly one comedy, “Ah, Wilderness!” With its broad swaths of rustic humor leading into a parable of redemptive love, “A Moon for the Misbegotten” could perhaps make the case for boosting that number up to 1.5. Certainly Kevin Spacey and his director, Howard Davies — who brought O’Neill to blazing life in their 1999 revival of “The Iceman Cometh” — have done what they can to accentuate the bright side of this “Moon.”

Their efforts, with Mr. Spacey’s James Tyrone Jr. (a barely fictionalized version of O’Neill’s brother who first appeared in “Long Day’s Journey Into Night”) masking his rapid dissolution through a vaudevillian, hat-slapping eagerness to please, are rarely boring and often insightful. But O’Neill, who watched his matinee-idol father squander his talent, and ultimately his happiness, on some 4,000 performances of a banal but lucrative audience-pleaser, would be the first to agree that such entertainment comes at a cost.

At risk here is, for my money, one of the truly great love stories of the 20th century, in any medium. That is the wary, bourbon- and guilt-fueled, unconsummated, cleansing romance between James and Josie Hogan (a splendid Eve Best), the towering earth mother who toils as a tenant farmer on his all but worthless Connecticut land. Violent and nurturing, promiscuous and pure, she offers a despondent James as well as herself a deliverance that is as evanescent and as illuminating as the full moon under which they drink and dream. The glories of this pairing are still there to be found and savored. But Mr. Davies’s suspiciously boisterous production of the 1947 play — which has imported its entire London cast, led by Mr. Spacey, Ms. Best, and Colm Meaney as Phil Hogan, the aforementioned coot — lets the bawdy first half suck up too much oxygen, diminishing the richer emotions that follow.

Those earlier capers are not to be slighted: As Josie and her reprobate father spar with each other, with their uppity neighbor, and finally with the desperately hearty James, a former third-rate actor, O’Neill allowed himself an uncharacteristic number of laughs and even a bit of slapstick. (The engaging Mr. Meaney, while lacking in some of Phil’s baser qualities, shines during these moments.)

But these gambols are tempered at all times by the possibility of James selling the farm out from under them and by the likelihood that he will drink himself to an early death. Phil and Josie, each for their own reasons, conspire to force James into a (literal) shotgun wedding. Ironically, it is this underhanded act that promises salvation for Josie.

Frank Rich memorably described Josie in the New York Times as “an almost mystical amalgam of mother, daughter, and virgin whore,” and while he didn’t necessarily mean it as a compliment, that combination has proved irresistible for actresses who either no longer are or never were wispy young things. “She is so oversize for a woman that she is almost a freak,” O’Neill writes of her on the play’s very first page, and yet the decidedly undersize, fine-featured Ms. Best embodies this “ugly overgrown lump of a woman” with ferocious, heartrending commitment. She’s at least a decade younger than most of the other famous Josies (Colleen Dewhurst, Wendy Hiller, Cherry Jones), and her coltish awkwardness and cracked, almost adolescent voice make Josie seem even less seasoned.

With her sinewy arms and faded print dress, she’s less the typical Rubenesque vision of fecundity and more an iconic Dorothea Lange image from the Great Depression. (Bob Crowley’s forlorn set design, with its precipitously leaning farmhouse and rusty farm bric-a-brac, accentuates the Dust Bowl parallels.) And yet Ms. Best, while up for the coy banter that punctuates so much of Mr. Davies’s production, summons every ounce of the scouring forcefulness that makes Josie’s and James’s transformation possible.

Early in the play, when a hungover James doesn’t know he’s been spotted walking up to the farm, Josie describes him staring at the ground “like a dead man walking slow behind his own coffin.” Later on, after much booze and after the two have crept closer to a mutual confession of love than they’ve ever allowed themselves, he admits that the real James is not behind the coffin but in front of it. “We can’t … escape ourselves no matter where we run away,” he says. “Whether it’s the bottom of a bottle, or a South Sea island, we’d find our own ghosts there waiting to greet us.”

In real life, James O’Neill’s ghost wouldn’t have long to wait. Eugene O’Neill set “Moon” in September 1923 — just a few weeks before his brother died after slipping into an alcohol-induced coma. Their mother had died less than nine months earlier, and the two deaths were clearly interwoven in the author’s mind, even some 20 years later. This becomes evident in James Tyrone’s climactic monologue about his shameful behavior immediately before and after his mother’s death.

This monologue, a tale of guilt-drenched licentiousness, is only slightly less triumphant than James’s parallel speech in “Long Day’s Journey.” Even during this scene, though, Mr. Spacey never lets the showman fade completely. A generous assessment of his antic delivery is that he is masking James’s self-loathing with a carefree façade. Still, it’s hard not to assume that he’s merely delivering a few extra easy laughs — and sidelining Ms. Best’s majestic efforts in the process. This sort of mooning about is more than just misguided. It’s misbegotten.

Until June 10 (256 W. 47th St., between Broadway and Eighth Avenue, 212-307-4100).