The musical version of Rocky is a technical knockout. Christopher Barreca's wondrous set features a regulation-size ring that rises, falls, and pivots to become a screen. Then, during the spectacular final fight, it slides out over the first eight rows of seats, and theatergoers are escorted to onstage bleachers that moments before doubled as the iconic stairs of the Philadelphia Museum of Art. In the viscerally realistic bout, choreographed by Steven Hoggett, peacocking champ Apollo Creed (Ragtime's Terence Archie) and our palooka of a hero (The Mystery of Edwin Drood's Andy Karl) make actual contact. No jazz hands, no kick lines, and the only singing comes from an unseen chorus reprising (of course) ''Eye of the Tiger.''
Despite the high-tech stagecraft, director Alex Timbers remains faithful to the indie spirit of the 1976 Oscar winner that made a star of Sylvester Stallone. Rocky's apartment is suitably dingy and the performances nicely understated, from buff and likable Karl (channeling Sly's mumble-mouthed diction) to mousy Margo Seibert as Adrian, the pet-store wallflower who captures his heart. At times the show plays less like a splashy Broadway musical than a Clifford Odets revival.
The best lines are lifted directly from Stallone's screenplay; Stallone shares credit for the show's book with Broadway veteran Thomas Meehan (Annie, The Producers), whose contributions include a cliché-heavy pep talk from grizzled manager Mickey (The Best Man's Dakin Matthews) that concludes: ''Go kid, go Rocky, run!''
The real trouble is that, unlike ''Eye of the Tiger'' or the snatches of Bill Conti's triumphal theme, Stephen Flaherty's bland new songs merely shadowbox at melody and never land the pop-rock punch they often seem to be seeking. Karl makes the most of his power ballad ''Fight From the Heart,'' and his duet with Seibert ''Happiness'' is pleasant enough despite her rather thin voice. But too many of Flaherty's songs play like missed opportunities, from Apollo's disco-tinged ''Patriotic'' to Mickey's nostalgic ''In the Ring.'' And Lynn Ahrens' lyrics, with clunky rhymes such as shoddy/body, are no help.
Even so, Rocky delivers edge-of-your-seat thrills particularly in the final 15 minutes that underscore the fact that fans of boxing and live theater share some DNA: They love to see their stars battered, bloodied, but still standing. B(Tickets: Telecharge.com)