Dissidents from rock conformity

Playing it safe isn’t for everyone in rock. Consider System of a Down and the Mars Volta, two uncompromising hard-rock acts that have somehow landed on the radio despite complex and confrontational sound signatures that no sane band would embrace as a ticket to the mainstream.

These are hard-rock bands with no rules, idiosyncratic and relentless, mingling melody and noise in disparate, surprising ways. On Thursday, in the first of two nights at the Long Beach Arena, these two L.A.-based acts continued to redefine what hard rock could be, minus the cliches and knucklehead sloganeering.

The night ultimately belonged to System of a Down, beginning its headlining tour with a crisp 100 minutes of music stretching back to the band’s 1998 debut album. As ever, the music was crowded with dizzying surprises and a raw elegance, shifting from hurried metal riffs to contemplative folk melodies, and from lyrics of great seriousness to startling absurdity.

System straddles two metal worlds, finding (or forcing) a link between Led Zeppelin and Slayer, with epic musical flourishes colliding with fried speed-metal riffs and a crazed jumble of words on politics, war, cocaine casualties and rough sex.

The band’s set began with guitarist Daron Malakian alone in the spotlight, plucking and singing the same delicate melody that opens System’s new album, “Mezmerize.” The band immediately shifted into the intense agit-pop of “B.Y.O.B.,” a blunt antiwar screed that sets angry shouts against mellow passages that could have been lifted from P-Funk, as singer Serj Tankian mocked happily: “Everybody’s going to the party ... dancing in the desert blowing up the sunshine.”

System’s newest material is easily among its best. Songs from “Mezmerize” and the upcoming “Hypnotize” show a band at a creative peak, or at least approaching one. In Long Beach, the songs “Violent Pornography” and “Lost in Hollywood” were blunt and surreal meditations on the media and damaged youth.

At center stage, Tankian was a typically commanding presence, with a range stretching from the occasional metallic Darth Vader howl to more complicated and emotional passages of near-operatic melody. He’s developed into one of hard rock’s finest vocalists, even as the frazzled shrieks of musical architect Malakian assume a higher profile, offering a startling and engaging contrast.

The concrete Long Beach Arena was not built for sound, and couldn’t match the warm acoustics that fans enjoyed at System’s benefit concert last April at the Gibson Amphitheatre. But the band’s energy and focus brought them close enough, from the hardest rock to Malakian’s brief moment again alone in the spotlight singing a verse of Neil Young’s “Hey Hey, My My.”

Soon enough, Malakian and Tankian were back together, harmonizing a quieter passage in “Violent Pornography,” a musical partnership potentially as influential as Page and Plant, and as crazily unpredictable as Bugs and Daffy.

Earlier on Thursday, the Mars Volta represented another significant collaboration -- guitarist Omar Rodriguez-Lopez and singer Cedric Bixler-Zavala -- during an hourlong set of explosive improvisations rooted in songs from its newest album, “Frances the Mute.”

The Mars Volta was a daring choice as the tour’s main support act, and a fitting one, though the band’s wild spasms of sound would be a challenge even to fans of System’s colliding elements. The Volta’s radio hits (“The Widow,” “L’Via L’Viaquez”) were just starting points -- stirring melodic pieces stretched out to free-jazz extremes and ‘60s acid-rock intensity, but never getting lost (or bored) in the ether. Playing it safe is no fun.