A relatively well-behaved Britney Spears wowed a crowd packed with superstars when she made a not-so-surprise appearance at Madonna's concert in Los Angeles Thursday night.

Wearing what the Los Angeles Times described as a demure tuxedo- style shirt, pants and black heels, Spears introduced herself with a take from her last album: "It's Britney Bitch."

She then sang along with Madonna on the last verse of the track Human Nature, to the delight of the crowd, which included Jennifer Lopez, Ryan Seacrest, Heidi Klum, Drew Barrymore, Fergie and Donald Sutherland.

But there was no repeat of their infamous smooch at the MTV Video Music Awards in 2003. Instead, Madonna graciously kissed Spears' hand as the troubled pop star left the stage.

Critics said it was her best performance yet in her bid to come back from the effects of her traumatic marriage break-up last year.

Later in the show, Spears' ex-boyfriend Justin Timberlake joined Madonna for a duet in front of the 50,000 fans who packed the Los Angeles Dodgers stadium.

Madonna closed the show with a multi-colored image of president- elect Barack Obama on her huge video backdrop. "We have something to celebrate," she said. "I don't know about you, but I'm the happiest girl."