NEW YORK (CNN/Money) - Viewers are about to discover just how broad Matt LeBlanc's shoulders are.

NBC Universal has not been shy about letting the world know that it has a lot riding on 'Joey,' the long-awaited 'Friends' spinoff starring LeBlanc as Joey Tribbiani.

The reason: NBC has long been a dominant primetime player, especially among the 18 to 49 year-old viewers that advertisers will pay top dollar to reach.

For three years running NBC has been the top destination for these sought-after viewers, allowing it to pull in more ad dollars during the annual pre-season sales of commercial air time than any other network.

Young adult viewers are "where the money is at," said Brad Adgate, senior vice president of corporate research at Horizon Media, a New York branding firm. "It's the only demographic that NBC cares about."

But with the twin departures last season of 'Friends' and 'Frasier,' NBC Universal risks losing that lead to either CBS, a Viacom (VIAB: down $0.01 to $34.70, Research, Estimates) subsidiary and the No. 1 primetime network overall for the last two seasons, or Fox, the News Corp. (NWS: down $0.09 to $31.33, Research, Estimates) unit whose ratings among 18 to 49 year-olds have been rising fast.

For months now, NBC Universal has been relentlessly planning for life after 'Friends,' the cheeky comedy about six twenty- and thirty-something year-old New Yorkers, which ended a phenomenal 10-year run last season.

Is one enough?

The network, owned by General Electric (GE: up $0.05 to $33.71, Research, Estimates), took the unusual step in May of showing advertisers and media buyers a full-length pilot. Summer viewers, especially those tuned in to NBC's broadcast of the Athens Olympics, have been flooded with promotions for 'Joey' and other season premieres.

Hoping to leverage its Olympics ratings momentum, NBC Universal pushed forward by three weeks its fall schedule. First up was 'Father of the Pride,' a cartoon comedy about white lions performing at the 'Siegfried & Roy' extravaganza in Las Vegas. NBC also debuted the fourth season of 'Scrubs' and premiered its new action series 'Hawaii.'

So far, it looks like the strategy is paying off. NBC dominated primetime against last week, with a 5.5 overall rating. ABC was second, followed by CBS and then Fox.

Thursday night is critical to NBC Universal's chances. On top of two comedies, 'Joey' and 'Will & Grace,' NBC will air the second installment of last season's surprise hit 'The Apprentice,' followed by the workhorse drama, 'ER.'

"They need Thursday to be their strong night," said Shari Anne Brill, vice president and director of programming at ad buying firm Carat USA. "Thursday was such a strong night for them so long that they used to get by without winning any other night of the week. The other networks used to roll over."

Not anymore. Both CBS and Fox have emerged as formidable competitors to NBC. For the last two seasons CBS, with "Survivor" and "CSI" on Thursdays, has edged NBC aside to lead the night.

Fox, too, is looking strong, Brill said, with its decision to move to Thursday nights 'The OC,' a night-time soap about beautiful people living in a tony enclave in Orange County, Calif.

Brill said Fox and CBS could draw viewers away from 'Joey,' but thinks the show has a shot at success. For one thing, she said, it's guaranteed to draw "disenfranchised 'Friends' fans" loyal to a character they know and love.

For another, by taking a character like Joey Tribbiani, relocating him to L.A., and introducing a whole new cast of characters, NBC Universal is merely following a formula that worked well with 'Frasier' and other sitcom spinoffs that have turned into hits.

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Brill, who's seen the full pilot, especially liked Joey's pugnacious sister Gina, played by actress Drea de Matteo (formerly of HBO's 'The Sopranos').

Two-thirds of all new shows won't be around by next year, Brill observes. "If the writing isn't there and the ensemble isn't there," she said, plunking old characters into new settings won't be enough to sustain a hit.

"I think NBC's lineup needed to be stronger," she said. "'Joey' is probably their best show."

That's quite a load on Matt LeBlanc's shoulders.