First you laugh your head off; then you open a vein. That’s the way it usually goes whenever “A Life in the Theater,” David Mamet’s 1977 lethal toast to American stage actors, is revived. But the darkness descends early in Neil Pepe’s staging of this backstage two-hander, which stars the stately Patrick Stewart as the veteran thespian who’s seen, done and survived it all and the watchable T.R. Knight as the young actor he mentors. Although the laughs still land, the affection that softens the satire is undercut by the melancholy tone struck in the first moments of the show.

Watching Stewart (“Macbeth”) take command of the gloomy backstage theater set (designed by Santo Loquasto and lighted to Stygian effect by Kenneth Posner) is enough to make you swoon. If anyone alive can embody the majestic weariness of a proud journeyman actor in the winter of his career, this hawk-faced, silver-throated thesp is a shoo-in.

So it’s more than a little disconcerting to observe Robert, the seasoned trouper Stewart plays here, so quickly revealing the self-doubt and emotional uncertainty beneath his autocratic professional demeanor. Amusing as it is to watch him ensnare an impressionable young colleague with false flattery of his “brilliant” performance (“I wouldn’t say it if it weren’t so”), his own need for validation is all too transparent.

Given the rather obvious desperation behind these insincere platitudes, it also takes some adjustment to accept the younger thesp’s willingness to be mentored by this sad old guy.

Knight, coming off five seasons on “Grey’s Anatomy” (and nice work in the 2001 revival of “Noises Off”), gives a poised, surprisingly subtle perf as John, the ambitious kid who seizes the opportunity to pick up a few tricks from Robert. But since he seems all too aware of his teacher’s personal and professional limitations, the trajectory of his apprenticeship is wobbly. In fact, John seems to have tuned out his mentor long before he tells him to “please shut up.”

Despite getting off on the wrong emotional foot, the production recovers once these hard-working thesps begin to throw themselves into their roles for the execrable shows in the company repertory. Mamet displays malicious glee in trotting out all the old chestnuts, from the World War I battlefield play (“Those dirty bastards, they stuck him on the wire and left him there for target practice!”) and the Chekhovian social drama (“If we could leave this afternoon … if we could just call, bring the carriage round, just leave this afternoon …”) to a definitive spoof of an English shipwreck drama, performed in thick lower-class accents (“Kid, we haven’t got a chance in hell. But you shouldn’t let it get you down, ’cause that’s what life on the sea is about”).

Helmer Pepe (“Speed-the-Plow”) is especially inventive when it comes to the onstage catastrophes that are the nightmare of every rep company: the broken fly zipper, the desk lighter that doesn’t light, the prop phone that doesn’t ring, the wig that flies off when its impassioned wearer is on the barricades in a French Revolution costumer. (Honors to Laura Bauer for the terrific costume parade and Charles LaPointe for some truly moldy-looking wigs.) Not to mention the missed cues, flubbed lines and unfortunate memory lapses.

Meanwhile, the backstage drama advances in brief scenes that catch those precise moments when tutor and pupil begin to switch roles. Both actors show canny judgment in those delicate moments, carefully but unobtrusively pacing out every incremental change in their relationship. Before you know it, John is no longer lending Robert his makeup brushes and Robert is lighting John’s cigarette.

Knight is properly heartless when John decides that he has learned all he needs to know about holding an epee and is ready to move on. For his part, Stewart shows heart, as well as great technique, in allowing Robert his dignity after he realizes John is no longer listening to his impassioned bluster about the joys and responsibilities of their noble art.

But if John is unmoved by his old mentor’s distress, Mamet isn’t, and there’s nothing sadder or sweeter than Robert’s last look around the house.

A Life in the Theater

Gerald Schoenfeld Theater; 1,071 seats; $121.50 top

  • Production: A Jeffrey Richards, Jerry Frankel, Jam Theatricals, Debbie Bisno, Eva Price, Larry Magid, Kathleen K. Johnson, Herbert Goldsmith Prods., Roger Kass, Barry & Carol Kaye, Kelpie Arts, Black-Pereira, Freedberg-Dale/Dombrowski-Manuel presentation, in association with Jeremy Scott Blaustein, Shane Marshall Brown, and Matthew Salloway, of a play in one act by David Mamet. Directed by Neil Pepe.
  • Crew: Sets, Santo Loquasto; costumes, Laura Bauer; lighting, Kenneth Posner; wigs, Charles LaPointe; fight choreography, J. David Brimmer; production stage manager, Matthew Silver. Reviewed Oct. 8, 2010. Opened Oct. 12. Running time: 1 HOUR, 30 MIN.
  • Cast: Robert - Patrick Stewart John - T.R. Knight