Arguably the greatest American musical, "West Side Story," lost the 1958 Tony for best musical to "The Music Man." Igor Goldin, who previously directed "Music Man" for the Engeman Theater, now has directed both shows on the Northport stage.

A side-by-side comparison proves -- again -- that "West Side Story" was robbed. (Credit where credit is due: book by Arthur Laurents, music by Leonard Bernstein, lyrics by Stephen Sondheim, based on Jerome Robbins' direction, choreography and concept.)

But a masterpiece that requires more than competent execution doesn't often measure up to its inspired source material. The Engeman's "West Side Story" is a rare, not-to-be-missed opportunity to truly appreciate an American theatrical treasure.

Oh, we could quibble about such anachronisms as slit-up-to-here mini-dresses on the girlfriends of the Jets. Or that Anita may not "pass" for Puerto Rican. But alternative casting adds to the rich fabric of this American-by-way-of-Shakespeare fable that feels so contemporary with immigration, street gang and firearm issues upfront today.

From the opening notes of the Jets-vs.-Sharks prologue, we feel the tension of a neighborhood transitioning from established immigrants to newcomers (Puerto Rican). Testosterone-fueled punks led by Riff (chest-thumping Sam Wolf) and Bernardo (lightning-tempered Nikko Kimzin) battle over turf.

Tony, the Jets' erstwhile leader now working at a drugstore, wants no part of their shenanigans. But after meeting a girl from the "other side," Bernardo's kid sister Maria, he falls instantly in love and obeys her entreaties to stop a fight between the gangs. His intercession (spoiler alert) leads to a "Romeo and Juliet" denouement, with an all-too-familiar modern twist.

Zach Trimmer as Tony and Samantha Williams as Maria are so appealing as a couple that their "Tonight" duet thrillingly reminds us of the hormonal power of first-sight love, heartbreakingly celebrated in "I Feel Pretty."

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As Anita, Karli Dinardo exudes defiance and vulnerability ("America," "I Have a Love"). Ashley Perez Flanagan delivers a dreamy "Somewhere" in the balletic ensemble number delicately choreographed by Jeffry Denman on DT Willis' abstract urban set (flawless accompaniment by James Olmstead's orchestra).

Each cast and crew member deserves plaudits. Sondheim, the sole surviving "West Side Story" creator, would be proud, we believe.

WHEN | WHERE 8 p.m. Thursdays and Fridays, 3 and 8 p.m. Saturdays, 2 p.m. Sundays through Nov. 8, John W. Engeman Theater at Northport, 250 Main St.

TICKETS $69-$74; 631-261-2900, engemantheater.com