Once upon a time, Britney Spears was a teenage sensation, a naughty sex kitten who fondled snakes, a Justin Timberlake dater and Madonna smoocher who scored undeniable eyebrow-raising hits, like 1999's "…Baby One More Time," that played a key role in creating the millennium pop universe we live in today.

Then, Britney Spears was a hot mess, an ex-Mouseketeer and former child star, stalked by the paparazzi, who fell apart in young adulthood, stumbled narcoleptically through a 2007 VMA performance, got caught shaving her head on video, and married Kevin Federline.

Now Spears, who began a three-night stand at the Borgata Hotel & Casino in Atlantic City on Thursday, is something else: A coolly proficient entertainer and hard-bodied celebrity survivor who retreated to Las Vegas for a four-year residency that she's taking on the road in her first concert tour since 2011.

These days, Spears operates far from the center of pop culture, and doesn't turn up on TMZ unless she's in a workout video with her muscly fitness-model boyfriend, Sam Asghari, or because K-Fed is asking for more child support for their two preteen sons.

It makes sense that for North American stretch of Spears' "Piece of Me" tour — named after a 2007 song that aimed to fight back against intrusive media scrutiny, in an evergreen strategy now being employed by Taylor Swift — is happening almost exclusively at casino venues. (Spears is also doing two dates at Radio City Music Hall next week.)

Britney Spears at the Event Center at the Borgata Hotel & Casino in Atlantic City on Thursday.
Dan DeLuca
Britney Spears at the Event Center at the Borgata Hotel & Casino in Atlantic City on Thursday.

The "Piece of Me" tour is very much a Vegas showroom act, a one-hour and 40-minute relentless operation that's well-suited to a mid-size sold-out venue filled with an almost entirely female audience who grew up on Britney.

Spears, now 36, was accompanied by a dozen dancers — six often shirtless dudes and six spangly dressed females. The well-rehearsed show, which she did for four years at Planet Hollywood until her residency ended this past New Year's Eve, moves inexorably in lockstep rhythm through seven sections, each broken up by a costume change.

The one-two punch of the ellipsis-happy turn-of-the-century hits "…Baby" and "Oops!… I Did It Again" — both of which were written by uber-successful Swedish songsmith Max Martin — came early in the show, both as punchy and irresistible as ever.

Spears moved confidently with (if not as lithely as) her dozen dancers throughout the impressive aerobic show. (Which began shortly after 8 with no opening act, don't be late!) She was also supported by a four-piece band on risers high above either side of the stage, consisting of bass, guitar, drums, and a keyboard player-slash-programmer.

Did she do her own singing? Yes, though much of it appeared to be prerecorded. Spears wore one of those impersonal Garth Brooks-Janet Jackson headset microphones, and worked hard putting dance floor-directed tunes like "Gimme More" (that's the one with the famous "It's Britney, B–!" aside) and the patently silly "If You Seek, Amy" across. But if you took a look on the choruses when her voice was reinforced, as if joined by several backup singers, you'd notice that no one else on stage was miked. It was the not-atypical sound in the modern concert production world of her own voice being multi-tracked.

Spears doesn't do a lot of chatting or connecting on a human level with the crowd, which stood throughout the night. The show's forward progress doesn't allow for much chitchat, the exception being a faux spontaneous huddle with two female dancers in which they decide to bring a male fan named Benny on stage for "Freakshow." He was target of dominatrix Britney's riding crop in a little playful BDSM action, where they got him down on all fours to be walked like a dog by his master. The volunteer was only too happy too oblige, and was deemed "so adorable." "I'm going to take him home with me," said Spears.

That number was representative of the evening in that it was mildly risque without being the slightest bit risky. Robotic is too strongly negative of a word — Spears seems to be enjoying herself throughout — but the show is mechanistic in its efficiency. Songs by will.i.am and a trio by Missy Elliott were played in changeovers to give the star a breather and the dancers a spotlight, while making sure there was no chance of the audience getting bored.

By the time the seventh act rolled around, all of the hits had been covered, including "Toxic," the Bollywood-flavored surf-guitar 2003 dance-pop meisterwerk. That song did not disappoint in its baroque presentation, and was followed by a medley of two more early hits, the grrl power anthem "Stronger" and teen romance banger "(You Drive Me) Crazy," bringing to a close an evening that's simultaneously highly energetic and a little uninvolving.