Because they are both teen pop stars from the '90s now trying to prove their adult credibility, it's easy to think of Justin Timberlake and Christina Aguilera as two sides of the same coin.
Heads, you've got a 22-year-old male singer eager to demonstrate that there is life beyond the sensationally popular boy band 'N Sync.
Tails, you've got a 22-year-old female singer out to convince us that she is more than "Genie in a Bottle," her featherweight 1999 pop hit.
To blur the distinction even further, both have sold almost exactly 2.6 million copies of their latest albums, and they are co-headlining a tour titled "Justified and Stripped" that opened a three-night stand Monday at the packed Staples Center.
But the similarities end there.
Monday's concert made it clear that this particular coin is really one-sided.
For sheer entertainment value, go with heads.
In a winning display of pure musical celebration, Timberlake turned out to be every bit as promising a solo artist as many industry sharpies -- not to mention shrieking young fans -- have predicted ever since the early days of 'N Sync.
Where he sang, danced and charmed his way through his set with ease, Aguilera's performance seemed as tedious as being trapped in a SigAlert. The chief problem is that she didn't convince us she knows quite who she is musically -- which is strange, since the point of her current album is to assure everyone that she is now her own person.
Although her racy outfits gave that album's title, "Stripped," another connotation, the record is supposed to lay bare the true Christina.
The petite singer has complained in interviews that her self-titled 1999 debut album didn't really reflect her -- that it was manufactured by record producers and others, and that she hated not being in control.
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In fact, the new album suggests that much in Aguilera's life has been on the troubled side, and the only way she can get past it is to share her pain with her fans. She has even gone from blond to brunet to make sure we notice that she's a new woman.
Before she stepped on stage Monday after a brief set by the "positive" hip-hop outfit Black Eyed Peas, Aguilera introduced the album's theme with a short video in which she sat strapped to a chair while such words as "lies," "tabloids," "press" and "rumors" flashed on the screen. But she is no quitter. She broke free, of course, and the concert began.
Relying heavily on material from "Stripped," Aguilera tried to make her story a universal, uplifting tale through such songs as the feminist-minded "Can't Hold Us Down," the fiercely accusatory "Make Over" and the self-affirming "Fighter."
Little of it was convincing because the songs (most of which she co-wrote) simply felt like generic expressions of anger and resolve, and the arrangements stayed within conventional R&B and pop boundaries. That left the music whiny rather than revelatory.
As a singer, Aguilera has long shown commanding range and power, but little of the restraint and taste that would let her touch rather than assault us. That's still true.
If the music reminded you of a budding diva (think Celine Dion and Mariah Carey) in places, the show itself seemed inspired in part by Madonna. Unfortunately, Aguilera has little of Madonna's physical authority or imaginative instincts for staging. Aguilera tried to interact with dancers on several numbers, but there was little sensual heat.
She did step away from all the show-biz theatrics at the end and tried to connect one on one with the audience by singing Linda Perry's "Beautiful," the centerpiece of the album.
Dressed more down to earth in jeans and a white T-shirt (the words "God Sees No Color" on the front), Aguilera wanted to be vulnerable as she sang, "I am beautiful no matter what they say / Words can't bring me down /I am beautiful in every single way."
It should have been a show-stopping moment, but it was too little too late. To make it work, Aguilera needed to define better just who she is, other than someone who very badly wants a career in show biz.
Timberlake's impressive showing was surprising considering how his solo album "Justified" and his videos have suggested a pop vision that begins and ends with the Michael Jackson of the '70s and '80s.
But Timberlake was born for the stage, and he has the savvy instincts to put together a show that works. Rather than make himself the constant center of attention, he was comfortable enough at times simply to be part of a talented ensemble.
Indeed, his band, which included a three-piece brass section, seemed a partner in his set rather than a backing unit as it laid down some contemporary pop, R&B and hip-hop textures that were as fresh and dynamic as something put together by an ace club DJ.
In some ways the actual songs seemed almost secondary to the joyful musical energy and spirit. At one point he interacted playfully with the band, taking the role of a human beat box as he danced on a crane high above the audience.
Like Aguilera, Timberlake co-wrote most of his songs, and he worked with some high-profile producers in the studio, including the Neptunes and Timbaland.
The difference is that he overcame the lack of depth in such new tunes as "Rock Your Body" and "Cry Me a River" by presenting them with a passion that was liberating in itself -- especially the falsetto touches on "Cry Me a River."
Timberlake acknowledged 'N Sync in a couple of places, but although he's still a member of that group, his eye is mainly on the future -- a heads up, if you will, that there is likely much more to come.
Justin Timberlake and Christina Aguilera
Where: Staples Center, 1111 S. Figueroa St., L.A.
When: Friday, 7:30 p.m.
Price: Sold out
Contact: (213) 742-7340