Many ways to play Wango Tango

Like a macrocosm of the songs it broadcasts, Top 40 radio is defined by a perpetually undulating blend of the expected and the unexpected. The fun -- and sometimes the thrill -- of listening is in catching weird juxtapositions of styles and sounds, and in hearing established pop stars rub elbows with who-sings-this? upstarts.

Saturday at the Verizon Wireless Amphitheatre in Irvine, L.A.’s Top 40 radio kingpin KIIS-FM (102.7) presented its annual Wango Tango concert, a five-hour marathon that offered the same combination of familiarity and novelty: business as usual spiked with an occasional surprise.

The night’s biggest shock? Kelly Clarkson, the original “American Idol” champ, known for her powerhouse vocal chops, was out-sung by Fergie, the Black Eyed Peas member known for her lovely “lady lumps.”

A big-voiced belter in the tradition of her fellow Texan Janis Joplin, Clarkson is a riveting performer, the sort who stalks the stage with purpose and feeling. Yet on Saturday she sounded -- and looked -- exceedingly ragged, as if exhausted by the effort of completing her latest album, due in July. Because it’s a punk song masquerading as a pop tune, Clarkson’s hard-rocking new single, “Never Again,” sounded great despite (or perhaps because of) the singer’s hoarseness.

But in older tracks such as “Behind These Hazel Eyes” and “Since U Been Gone,” Clarkson’s depleted voice prevented the music from generating any emotional heat.

A little later, Fergie gave her fans a condensed version of the tightly choreographed show she toured with the Peas last year; BEP mastermind will.i.am (who produced much of Fergie’s solo debut, “The Dutchess”) even showed up to help sing “My Humps.” But then the Hacienda Heights native whipped through a remarkably faithful version of Heart’s “Barracuda,” which made it seem as though Fergie has been spending more time lately singing in dingy rock dives than making glossy pop-rap videos.

Other artists were less interested in upending the capacity crowd’s expectations. Ludacris ran through a typically rowdy set of his ribald rap hits, including a medley of older material he performed to make sure everyone was as well-versed in Ludacrisology as he thought they should be.

Accompanied only by a DJ, Cuban American MC Pitbull went the medley route too, delivering a few verses of each of his furious party-rap jams. His was the least complicated set of the night, yet Pitbull engaged the audience more readily than anyone else Saturday. It’s not easy to make a 16,000-capacity amphitheater feel like a club; Pitbull had no problem doing it.

On a less-aggressive tip, Robin Thicke led a lithe four-piece band through three of his R&B; slow jams, while Elliott Yamin, another “American Idol” alum, demonstrated his love of old Stevie Wonder records.

A more exciting -- if also more uneven -- performance came from Gym Class Heroes, an amiable rap outfit from upstate New York that has cultivated a large following in the emo scene. Before he launched into a sloppy rendition of “Cupid’s Chokehold,” the Heroes’ Supertramp-sampling hit, frontman Travis McCoy declared that the love song was a rejoinder to the recent wave of emo tunes featuring “boys singing about how some girl broke their heart.” You have to wonder what spurred McCoy to bite the hand that feeds him.

Enrique Iglesias, who played a tidy set of Latin-inflected disco-rock, didn’t provide much in the way of a surprise, but he did receive one when he pulled a female audience member onstage during “Hero,” his tender 2001 smash. Iglesias’ usual shtick is to give the lucky lady a kiss at the song’s conclusion. In Irvine, though, the young woman revealed that she was only 16. Forced to improvise, Iglesias made do with an avuncular peck on her cheek.