Were there any doubts that “The Friel Project,” Irish Repertory Theatre’s series honoring one of the 20th century’s great playwrights, would prove one of the highlights of this theater season, they have pretty much been laid to rest. Following its superb productions of “Aristocrats” and “Translations,” two of the various works that secured Brian Friel’s reputation as his country’s answer to Chekhov — and in advance of a revival of “Molly Sweeney” due later this spring — Irish Rep has just unveiled the project’s most moving entry yet.

“Philadelphia, Here I Come!” was first produced at Dublin in 1964, more than a decade before either of the previously mentioned shows had their premieres. Like those later plays, and numerous others Friel wrote, it’s set in the fictional town of Ballybeg — though, as the title suggests, America beckons its young protagonist, Gareth “Gar” O’Donnell, as it did his creator: “Philadelphia” would mark Friel’s Broadway debut and earn him his first Tony Award nomination, in 1966.

The 25-year-old Gar has dreams of his own: “Philadelphia” unfolds on the night before he’s set to leave his small town for the titular city, where he’s secured a job working at a hotel. It may not be as glamorous a gig as the one that brought Friel to New York, but Gar is excited, and anxious — though his eagerness and trepidation are tinged with no small measure of melancholy.

That’s because “Philadelphia” is, at its heartbreaking core, the story of Gar’s failure to establish a loving bond with his father, an aging, emotionally constipated widower who lost Gar’s much younger mother just days after their son was born. To evince the crippling impact this has had, Friel divided his central role into two parts: a “public” Gar, the one other characters can see and hear, and a “private” Gar representing his inner voice.

In Irish Rep’s new staging, masterfully helmed by producing director Ciarán O’Reilly, that voice is relayed by a young musical theater veteran, A.J. Shively, whose formidable footwork was a high point of Broadway’s overstuffed “Paradise Square.” As Private Gar, Mr. Shively gets a more modest but wittier showcase for his song-and-dance skills — both Gars sing, and here they also jump and prance about nimbly — as well as a vehicle for his considerable gift with accents. His Gar, in dialogue with his public self, imagines himself in roles ranging from a posh British radio announcer to an old-school Hollywood screen siren.

Yet Mr. Shively’s turn is most compelling, and shattering, for the emotional intuition he brings both to exchanges with Public Gar — played here by David McElwee, who captures the character’s sensitivity and excruciating loneliness to devastating effect — and those passages in which Friel allows us to watch Gar observing himself. 

As Gar struggles repeatedly to connect with others — a love interest, lads in his town, the aunt who wants him to join her and her husband in America — both actors summon, often wordlessly, emotions ranging from horror to shame to frantic glimmers of hope.

Mr. O’Reilly himself plays Gar’s dad, S.B. O’Donnell, known as “Screwballs” to his son. He delivers a performance that is harrowing in its discretion; a climactic scene in which the O’Donnells seem to finally approach something close to communication left me with my heart in my throat, until it seemed to descend into my stomach.

Other standouts in the flawless company include Deirdre Madigan, cast as Gar’s aunt, whose garrulous manner hides a burning emptiness stemming from childlessness, and Terry Donnelly, marvelously dry and, in the end, poignant as the O’Donnells’ long-suffering housekeeper. Patrick Fitzgerald makes a haunting appearance as one of Gar’s old teachers, who once courted his mother and now avidly supports the young man’s relocation.

“I gather it’s a vast, restless place that doesn’t give a curse about the past,” the older man tells Gar, referring to America. “And that’s the way things should be.” Yet as “Philadelphia, Here I Come!” reminds us, neither roots nor scars can be simply shaken off, and I doubt that message has often come across more powerfully than it does here.