Spears, 32, has signed on to perform 50 shows each in 2014 and 2015 at the Planet Hollywood Resort and Casino.
She cuts a different figure from the typical Strip headliner. Other successful Las Vegas acts— including Shania Twain, Elton John and Celine Dion— have generally attracted an older audience. Judging from Friday's show, her fans are more likely to be found at a casino mega-club than in front of a slot machine.
Still, "Piece of Me" is not immune to nostalgia, one of the prime currencies in Las Vegas entertainment. It includes several callbacks to the 1990s and early 2000s, including plaid shirts tied around dancers' waists and a recap of the skin-tight sparkling bodysuit Spears wore in the "Toxic" music video.
Spears' younger self haunted the show, with clips of her early performances playing on huge monitors. Notably absent from those monitors, to the displeasure of some fans in the cheap seats, were any live close-ups of what was unfolding onstage.
On his way out, Shane Sodeman, of San Diego, complained that Spears hadn't donned the sexy school girl outfit or the skintight orange jumpsuit she wore in sexier days. A version of the suit was on display in the lobby.
Speculation abounded ahead of the show that Spears would not be singing live, a claim that officials with Planet Hollywood parent company Caesars Entertainment Corp. denied.
Entertainment Programming Vice President Kurt Melien said Spears sings against a recorded track of her vocals to help her through the more physically grueling parts of the set, and add the electronic undertones that characterize many of her songs.
On Friday, all but a few performances seemed to require intense athleticism. Some audience members said it would be unfair to require Spears to perform a high-intensity workout on stage and also hit every note. Given a choice between the two, they said they'd take the choreography.
Maryn Harberg, 29, spent the night dancing in her $139 seat, on the upper end of the $59 to $179 scale. She'd come to the Strip for just one night, for Britney.
"I loved it," said the beaming Boston resident. "She was totally lip-syncing, but that's what she does, she puts on a show."
Spears has lost some of the crisp precision that characterized her dancing a decade ago, but she was in constant motion during the show, allowing her backup dancers to throw her through the air, and flying around in a huge angel costume for a performance of "Everytime."
She spent downtime marching around stage and posing, banishing the specter of her disastrous 2007 MTV performance, which also took place in Las Vegas and was a career low point.
Younger divas Selena Gomez, Miley Cyrus and Katy Perry lent moral support from the audience.
Casino executives say the gig may be extended if it proves a success.
Hannah Dreier can be reached at http://twitter.com/hannahdreier.