A most angst-ridden Christmas

The ho-ho-horror.... The ho-ho-horror....

Well, what do you expect when you celebrate the Christmas season with Nine Inch Nails and Korn?

Those bands and to a lesser extent System of a Down brought a sack full of angst to the first night of the 16th annual KROQ Almost Acoustic Christmas concerts at Gibson Amphitheatre on Saturday.

NIN’s Trent Reznor and Korn’s Jonathan Davis are two of the most cathartic performers in rock, upchucking a lifetime of inner torment and forming it into music of overwhelming force. Even though both have turned to slightly more conventional approaches on their latest albums, onstage there was no compromise in their enraged exorcisms of betrayal, hypocrisy and abuse.

Korn marked the evening’s turn from warm-up time to major event, returning from a period of transition in which it changed record companies, lost guitarist Brian “Head” Welch (to the Lord, of all things) and collaborated with the pop-stained writing-production team the Matrix for its new album, “See You on the Other Side.”

None of that seemed to affect the Bakersfield-bred band’s performance Saturday, as it took the stage to the most avid welcome of the evening. With its menacing biker look, outlaw charisma and us-against-the-world attitude, Korn is the Oakland Raiders of rock, a team that’s in the league yet somehow apart from it.

Korn didn’t suffer any loss of depth or power playing as a four-piece, mounting a rich, loamy sound whose textures had no trace of harshness. It was like a massive, weighty cloud of anger and anguish.

Davis’ gnarled vocals sometimes turned into a guttural chatter, but he also flashed a bit of crooning at the end of the new “Liar.” The audience seemed to receive this gentler side of Korn with no trace of anti-pop hostility.

Nine Inch Nails has been another comeback story this year, with Reznor going sober and reclaiming his position as rock’s poster boy of pain. His retooled band elevates rock guitar and demotes electronics and keyboards, suiting the more hook-focused nature of the songs on the “With Teeth” album.

Reznor and company have already made their statement in Southern California this year, with memorable appearances at Coachella and the Hollywood Bowl, so the Acoustic Christmas spot was more in the way of summation. But the band played a take-no-prisoners set, an unrelenting hour-plus powered by percussive, staccato guitar-thrashing from Reznor and Aaron North and punctuated by much hurling of instruments.

For their own sake and that of anyone nearby, let’s hope Davis and Reznor aren’t disappointed come Christmas morning.

System of a Down, which closed the six-hour show, has already cemented its status as unassailable creative force and beacon of integrity this year, putting out a long, ambitious album in the form of two separate releases, “Mezmerize” and the new “Hypnotize.” Saturday’s set was a fitting finale, a daunting, dazzling display of its idiosyncratic music.

That triple play was a piece of perfect programming for KROQ, three bands that defined the story in heavy music this year, connect deeply with their audience and are different enough to keep things interesting.

Things didn’t go quite so smoothly in the first half of the evening, when some instances of mistaken musical identity, mismatches and technical gaffes made for some spotty going.

This year’s shows were cleanly divided between Saturday’s voices from the void and the sugar plum fairies (Coldplay, Depeche Mode, the White Stripes, et al.) billed on Sunday, but Fall Out Boy, which ended the pre-Korn preliminaries Saturday, might have been better suited for Night 2.

The band, whose hit album “From Under the Cork Tree” led to a Grammy nomination for best new artist last week, is loosely classed as emo, and early in the set bassist Pete Wentz noted that they probably seemed a little “flaming” -- maybe meaning that their buoyant sound relies on catchy guitar and vocal hooks, and their lyrics are more clever than purgative (“I’m just a notch in your bedpost / You’re just a line in a song”).

Add to that poor fit a sound problem that stifled their guitars for a spell, along with mounting impatience from Korn fans (who can be as menacing-looking as their heroes), and you had one of those what-am-I-doing-here sets that pop up periodically at Acoustic Christmas.

To their credit, the band didn’t back down. Wentz acknowledged the crowd’s disaffection, reaffirmed the group’s pride at playing the show and dedicated the last song to everyone who’s in a band before stepping out onto the teeth of that audience.

Thrice, which preceded Fall Out Boy, brought out a string section as a special Christmas touch, but because of a technical glitch neither the string section nor singer Dustin Kensrue’s acoustic guitar could be heard for much of “Stare at the Sun.” Overall, the Orange County band seemed shy and somewhat shambling, largely because it followed a flamboyant set by Avenged Sevenfold.

This Huntington Beach band, whose stock is rising in the metal world, was the only group on the show (opened by the earnest but undistinctive Rise Against) to come off as merely an act -- a glam-goth-macho mix preoccupied with preening and posing. The musical attack was tight and the double kick-drum fusillades could pin you to the floor, but there wasn’t a glimmer of the kind of soul that would be bared repeatedly and compellingly a few hours later.