Perhaps inevitably for a documentary spoof chronicling an exercise in (albeit fictional) endurance, “7 Days in Hell” starts with considerable promise before gradually running out of gas. A clever satire of those ESPN “30 for 30” and HBO Sports documentaries, the special — basically a featurette at 42 minutes — covers an epic Wimbledon tennis match between Aaron Williams (Andy Samberg) and Charles Poole (“Game of Thrones’ ” Kit Harington). It’s a fine idea, although in terms of the less-is-more quality that characterizes much of Samberg’s work, “4 Days in Hell” would have almost surely been more satisfying.

Much of the fun involves the cameos by actual tennis and sports luminaries, including Chris Evert, Serena Williams, John McEnroe and Jim Lampley. Those are augmented by actors hamming it up, such as Michael Sheen as a lascivious, bloated TV host or Mary Steenburgen as Poole’s mom, as the talking heads reminisce about the unprecedented match, which, through a series of increasingly absurd events, lasted for an entire week.

Samberg’s Williams — adopted, we’re told, by Venus and Serena’s dad Richard, in what the latter hysterically calls “a reverse ‘Blind Side’ ” — is tennis’ enfant terrible, a bad boy with a Bjorn Borg-style hairdo whose misbehavior lands him in prison. Poole, meanwhile, is a near-moron (he tries vamping his way through interviews by simply repeating the word “indubitably”), who is destined to be the U.K.’s first Wimbledon champ in decades, a breakthrough that elicits slurry latenight phone calls from the Queen.

Written by Murray Miller and directed by Jake Szymanski, “7 Days” exhibits a persistently naughty streak, such as animated illustrations of the orgies in the prison where Williams was held. Yet the humor begins to feel more labored as the producers endeavor to extend the contest through delays ranging from on-court sex acts to an impromptu appearance by magician David Copperfield, playing himself, as one of Williams’ partners in debauchery. Simply put, the mockumentary’s wryness and faux earnestness — including direct-to-camera interviews — begin to fray as the situations become more and more ridiculous.

Everyone involved seems to be having a good time, which certainly counts for something. Still, in today’s age of rapid-fire comedy, there’s an art to recognizing just how much mileage can be wrung out of an idea. By that measure, “7 Days in Hell” has its share of strong points, and given the marquee names involved, it’s easy to see why HBO would provide subscribers with a courtside seat. That said, the highlights are offset by enough faults, as the match drags on, to prevent this from being scored as a clear-cut winner.

TV Review: ‘7 Days in Hell’

(Special; HBO, Sat. July 11, 10 p.m.)

  • Production: Produced by Murray Miller Prods., Young Sandwich and Buss Co.
  • Crew: Executive producers, Andy Samberg, Murray Miller, David Bernad; co-executive producer, Jonathan Buss; director, Jake Szymanski; writer, Miller; camera, Craig Kief; editors, Dan Marks, Pat Bishop; casting, Hayley Simpson Marcus. <strong>42 MIN.</strong>
  • Cast: With: Andy Samberg, Kit Harington, Fred Armisen, David Copperfield, Lena Dunham, Chris Evert, Will Forte, Karen Gillan, Filip Hammar, Jim Lampley, Howie Mandel, John McEnroe, Soledad O’Brien, Michael Sheen, Mary Steenburgen, June Squibb, Serena Williams. Narrator: Jon Hamm
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