When Audra McDonald’s Josie Hogan embraces Will Swenson’s James Tyrone in the last act of Eugene O’Neill’s elegiac masterwork “A Moon for the Misbegotten,” it’s an act — and a performance — of profound love, understanding and grace. This barefoot madonna may be raw, rough and randy for most of the play, but at this moment her open heart knows this broken man most needs peace before dying. The six-time Tony winner also knows what the role needs to get her to that transformative moment in the excellent Williamstown Theater Festival production. In her freshman go-round with O’Neill, McDonald goes to the head of the class in a full-bodied, sure-footed and deeply moving performance that is destined to be have further life beyond the Massachusetts Berkshires’ annual stage festival.

In this production, the Hogans, the Connecticut farm tenants of the landlord Tyrone in 1923, are not a shanty Irish family as originally written but rather a poor black brood, now reduced to a wily father and his take-charge daughter barely surviving on rock-strewn land in a shack of a house. Though the brogues have been dispensed with, the cavernous class divide still holds true — and may be even more relatable for contemporary audiences.

The play, written in 1943 and first produced disastrously four years later (it found its place in the theatrical firmament years later), begins as a rustic comedy before it turns, in the second act, into a haunting night of the soul. Director Gordon Edelstein stages this production with assurance, making the most of both the lighthearted scenes and the dramatic anguish of the protagonists, while also discovering quieter, private moments of reflection and realization.

He is greatly assisted by Ming Cho Lee’s original design from an earlier production, and adapted for the WTF stage by Lee Savage, realistically depicting an unforgiving setting against a slightly surreal and troubled sky. Jennifer Tipton’s exquisite lunar (and sunrise) lighting and John Gromada’s soundscape also are pluses in the production.

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