What happened?

How does a musical move into a theater more than 1,000 seats smaller and get broader in its delivery? How does a director who worked on the original production of a classic, who literally wrote the book on it, allow scene after scene to collapse into mood-shattering mayhem on his watch? How does a glorified summer-stock presentation emerge with the energy and discipline of a Broadway hit, and the resulting Broadway transfer meander with the diffuse, undermotivated energy of summer stock?

How on earth, in other words, has the benighted revival of “Gypsy” that opened last night been allowed to happen?

In one of the more puzzling and dispiriting developments to reach Broadway in some time, Arthur Laurents’s staging of the acid-etched 1959 valentine to show business has managed to shed nearly everything that made its previous iteration — a keenly anticipated three-week run last summer at City Center — so cherished. That production, notable for finally unleashing Patti LuPone in the role of the comparably formidable Mama Rose, has grown in every possible direction — and not in a good way.

The emotional punch that has earned “Gypsy” its status very near or possibly at the top of the list of great American musicals remains largely undimmed. With Jule Styne’s score, Stephen Sondheim’s lyrics, and Mr. Laurents’s book offering a still unmatched blend of toe-tapping excitement and harrowing family drama, how could it not? Rose’s vicarious, daughter-warping drive for Depression-era stardom has long served as a metaphor for the corrosive pressures of success-at-all-costs America. This steamroller in stockings, armed with immortal songs such as “Small World” and “Everything’s Coming Up Roses,” was and is an iconic encapsulation of the brassy yet vulnerable energies that fuel the spangled dream factory of Broadway.

“You make ’em beg for more,” she advises her long-neglected younger daughter, Louise (Laura Benanti), “and then don’t give it to them!” Louise, of course, ignored the last half of that suggestion, morphing into the legendary stripper Gypsy Rose Lee and achieving a notoriety that would both scandalize and vindicate her mother. Ms. LuPone, along with virtually her entire cohort of talented and misguided performers, gives and gives and gives until the only sensible response is to beg for no more.

Mr. Laurents largely replicates the crystalline staging of the original director/choreographer, Jerome Robbins, as he did in Broadway revivals in 1974 and 1989. (The Bernadette Peters mounting of 2003 was an awkward hybrid of Robbins and Sam Mendes.) Apart from incorporating Patrick Vaccariello’s unimpeachable 25-piece orchestra onstage, as is common for shows that originated as part of City Center’s Encores! series, the only substantial modifications involve the excision of a few minor bits of dialogue.

The damage takes place within this durable framework: Mr. Laurents displays an astonishing lack of trust in the material that has worked for a half-century, nudging pros like Ms. Benanti and — as Rose’s long-suffering beau Herbie — Boyd Gaines into distracting paroxysms of body-wiggling glee, lip-trembling grief, and table-slamming frustration. The forced bonhomie in the giddy trio “Together, Wherever We Go” sorely tries the patience, as do the extended stretches of (intentionally) dreadful vaudeville acts, while Rose and Herbie’s hands-and-knees cavortings during “You’ll Never Get Away From Me” are just bizarre.

The supporting roles have been written to make lasting impressions in limited stage time, so it is perhaps not surprising that a few of these actors seize the opportunity. As a trio of jaded strippers, Alison Fraser, Lenora Nemetz, and a near-comatose Marilyn Caskey — whose “I’m electrifying / And I’m not even trying” couplet has never rung so true — grab every ounce of lowbrow ebullience from “You Gotta Get a Gimmick.” (The sequence also gives Martin Pakledinaz’s terrific costumes a deserved turn in the spotlight.) And Leigh Ann Larkin continues to bring an eerie intensity to the often benign role of June, Louise’s coddled older sister. As for the domineering, resourceful stage mother at its center, though, this Rose makes little effort to contain her rage or joy or anything else.

Ms. LuPone’s rapacious energy remains the closest modern-day corollary to that of Ethel Merman, the original Rose, and her dexterous voice and ear for textual nuance go Merman one better. This uncanny blend of fury and finesse emerges exactly twice in Ms. LuPone’s latest go-around: once very early on, when she spills out her dreams with hypnotic speed during “Some People,” and once near the end, when she silently (if prematurely) comes to grips with the idea that those dreams may finally be over. In between, though, Ms. LuPone has taken on a sizable array of audience-pleasing flourishes and lowest-common-denominator gambits. These culminate in Messrs. Styne and Sondheim’s magisterial mad scene “Rose’s Turn,” now complete with dropped lyrics, little-girl voices, and a meltdown that starts at maximum volume and builds to unsupportable heights. Here’s what I wrote about Ms. LuPone’s performance last summer:

“If I could’ve been, I would’ve been,” Rose laments after “Rose’s Turn,” her shattering aria of abandonment, ‘and that’s show business.’ Well, Ms. LuPone could and should be a Rose for the ages. And she is.”

Or, rather, she was, before her Rose devolved into a mannered dervish, with just enough flashes of that original brilliance to remind us what has gone away. That, I suppose, is show business. It is also very sad.

Open run (246 W. 44th St., between Broadway and Eighth Avenue, 212-239-6200).