Theatre games are serious business in Annie Baker’s achingly funny and blisteringly heart-breaking new play, Circle Mirror Transformation. The much buzzed-about production has been extended for two additional weeks at Playwrights Horizons due to popular demand (and critical hosannas).

At a community center in the fictional town of Shirley, Vermont (also the locale of many of Baker’s other plays, including Body Awareness which played last year at Atlantic Theatre's Stage 2), five adults participate in an acting class. In what at first appears to be theatrical nuttiness á la the film Waiting for Guffman, the disparate group plays improvisational theatre games during classtime, fall in and out of love during breaks, and discover uncomfortable truths about themselves and each other over the course of the six week-long class.

Circle Mirror Transformation is catnip to actors –theatrically-inclined audience members chuckle at the recognition of the touchy-feely exercises and characters’ questioning of when they were going to do some REAL acting, while director Sam Gold’s crackerjack cast revel in Baker’s script – this is the type of show in which what is not spoken screams louder than any bit of dialogue ever could. Glances, awkward silences, a shift of the eyes or body, crossing the arms, and hands stuffed in pockets say volumes about these five lonely characters and their evolving relationships with each other.

It’s tough to imagine a better cast. As the class’s instructor, Dierdre O’Connell is all Stanislavsy-inspired theatrical eccentricity, but imbued with a real sense of gravity as her improvisational games tell her more about her husband (gamely participating in the class, played by Tony nominee – and Drama Desk nominee for Baker’s Body Awareness – Peter Friedman) than she would like to know. Heidi Schreck portrays a thirty-something wanna-be actress transplanted from New York who is smarting from a failed relationship, and Reed Birney is Schultz, a local furniture-maker whose recent divorce has also left him with a hole in his heart. Schultz’s devastating reaction to being eliminated from a childish game is simultaneously funny and devastating. And as Lauren, a teenager who takes the class to prepare for her high school’s auditions for West Side Story, Tracee Chimo is an absolute delight with facial expressions worthy of silent film comedy titans.

In the final scene, as Lauren and Schultz imagine an encounter ten years in the future, Chimo’s character evolves from an introverted girl who hides like a turtle in the shell of her hooded sweatshirt to a self-assured young woman, clear-eyed about the past and present. This transformation is the stuff of great theatre. Much like the rest of Circle Mirror Transformation.

The performance schedule for CIRCLE MIRROR TRANSFORMATION is Tuesdays through Fridays at 7:30 PM, Saturdays at 2PM & 7:30 PM and Sundays at 2PM & 7PM. Tickets, $50, may be purchased online via TicketCentral.com, by phone at (212) 279-4200 (Noon-8pm daily), or in person at the Ticket Central Box Office, 416 West 42nd Street (between Ninth & Tenth Avenues). For more information: www.playwrightshorizons.org.