John Mayer's Monday night show at Los Angeles' famed Viper Room was supposed to be a surprise, but his name on the marquee removed any air of mystery. Still, the singer-songwriter had some surprises in store for the capacity crowd.

Taking the stage a little after midnight, Mayer launched into a lengthy blues instrumental that showed off his considerable guitar chops. "I'm just gonna chill out and relax," he said from the stage.

A blues enthusiast, Mayer channeled the spirits of everybody from Albert King and Buddy Guy to Jimi Hendrix, playing both "Axis Bold as Love" and "The Wind Cries Mary." Doing his best Stevie Ray Vaughan, Mayer so impressed the crowd that ZZ Top's Billy Gibbons, a guitarist who knows something about the blues, jumped on stage and shouted repeatedly, "Give it up for my boy!" This seemed to surprise even Mayer, who said, "I don't know what the hell is going on. Hello, Mr. Gibbons." But, as Mayer later pointed out, "This is a blues jam and that means there's no structure."

Near the end of the hour-plus set, vocalist David Ryan Harris joined Mayer and released the guitarist's funky side during an extended jam of Michael Jackson's "Wanna Be Starting Something."

Mayer, who played until nearly 1:30 a.m., thanked the crowd for letting him indulge himself. "I know I have the best fans in the world," he said, "because they let me play whatever I want whenever I want."

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