After a few songs at Madison Square Garden on Wednesday night, Justin Timberlake needed a break. Like a man who had just spent a hard day hip-thrusting at the office, he shrugged off his white suit jacket. Loosened his tie. Rolled up his sleeves. Then he kicked back with a relaxing tequila shot. He hadn’t played the Garden since 2000, with ’N Sync, and his return certainly deserved a toast with the band.

As the drink went down, he screwed his face into a grimace. “I felt like such a man before I took that shot,” he said. “Kids, don’t try that at home.”

The Old Justin, an earnest, cred-deprived crooner with a boy-band past, is still coming to terms with the New Justin, a racy pop superstar who can mock Prince and get away with it. Last year his addictively catchy album, “FutureSex/LoveSounds,” sold about 2.5 million copies and was showered with critical acclaim.

He had two monster hits, the R&B; ballad “My Love” and the buzzing dance track “SexyBack,” responsible for one of 2006’s biggest catchphrases: “I’m bringing sexy back.” In December he even won the respect of teenage guys, thanks to a naughty R&B; spoof with Andy Samberg on “Saturday Night Live.” Given that it involves gift boxes and the male anatomy, its title is unprintable. And given that it involves gift boxes and the male anatomy, it is a huge hit on YouTube (13.6 million views and counting).

But 2007 is already better for Mr. Timberlake. He enjoyed good reviews for “Alpha Dog,” which appears to be a movie about his bare torso. He is up for four Grammys on Sunday, including for album of the year. And since his reported split from Cameron Diaz, he is Hollywood’s new A-list bachelor prize. If the celebrity weeklies are to be believed, buxom thespians are fighting for his affections. Even Donald Trump paid his respects at the sold-out Garden show, offering a presidential wave for the camera phones.

With his slight frame and baby face, Mr. Timberlake is not an obvious candidate for pinup status. Essentially a well-mannered Southern-boy-next-door, he doesn’t embody much mystery or menace. If someone pushed him too far, he would probably just smash a disco ball. But since his last tour, for 2002’s multiplatinum “Justified,” he has learned how to project sex-symbol edge. During an ambitious, well-oiled spectacle of nearly three hours, this New Justin cursed, gyrated and mimicked bedroom acts with his lingerie-clad dancers (although he avoided any wardrobe malfunctions). He filmed himself with a hand-held camera as his band jammed to “What Goes Around,” making demonic “Blair Witch Project”-style faces. Then he raised his middle finger.

But the Old Justin swooped in regularly to reassure the tweens. During “Summer Love” he cooed, “I can’t wait to fall in love with you.” During “My Love” he asked, “Would you date me on the regular?” During “Cry Me a River,” a break-up ballad, he moaned, “Why did you leave me all alone?” No wonder the female screams were so bloodcurdling: he’s a rock star who can commit.

At first the show was riveting. There was a round stage in the middle of the floor, surrounded by a curtain that often doubled as a video screen. (As Mr. Timberlake sang “Losing My Way,” about a crack addict named Bob, a ghostly gospel choir appeared on the scrim.) Band members flanked both sides of a giant riser where Mr. Timberlake and his backup posse performed elaborate line dances. Mr. Timberlake is remarkably fluid; at one point he jerked back and forth as if he were a slab of vinyl being scratched by a D.J. Suddenly, Timbaland, the brilliant producer behind “Future/Sex,” appeared to rap along to a kinetic version of “Chop Me Up.” Then he took over as Mr. Timberlake disappeared for an inexplicably long, energy-sapping break.

As “scary” imagery bombarded the video scrim (monsters, Venetian masks, Nelly Furtado), Timbaland played snippets of classics like Michael Jackson’s “Billie Jean” and Jay-Z’s “Big Pimpin.’ ” But he rarely found a danceable groove. People sat down or wandered about until an R&B; version of Kelly Clarkson’s “Since U Been Gone” inspired an arena singalong. Timbaland closed his set with the video for “Give It to Me,” the new single from his album, due in late March. And — synergy! — guess who guest stars?

Mr. Timberlake, now sporting black pants and vest, returned with the upbeat “Rock Your Body” and some liquid break-dancing moves. Just as things picked up steam, he immediately shifted into an overlong ballad sequence, sitting at the keyboard for a “couple of songs that mean something very special to me.” (They included “Easy” by the Commodores.) But it’s not as if anyone was going to leave. For one thing, he was required to do “SexyBack.” And the buzz was that Mr. Samberg would be a surprise guest.

Sure enough, an M.C. appeared to salute the “biggest video on YouTube.” Mr. Timberlake and Mr. Samberg ran onstage dressed as tacky boy-band lotharios, with Christmas presents strapped to their groins. “Number one, cut a hole in a box,” they directed. (Let’s leave instructions two and three up to the imagination.) The crowd roared its approval, and Mr. Timberlake started laughing. But Old Justin was not about to send the ladies home like this.

Mr. Timberlake reappeared in a T-shirt for one last ballad, proclaiming himself a simple guy from Tennessee. “There’s a one in a billion chance that something like this happens,” he said, confident enough to know he got what he deserves.