A Chemical combustion

AS the curtain rose on Tuesday’s Halloween performance by My Chemical Romance at Hollywood’s House of Blues, the group’s holiday-appropriate attire was greeted by rapturous applause. Members of the pop-punk quintet dressed identically in black marching-band jackets; their faces covered with a thick application of greasepaint to resemble grinning skeletons.

“Happy Halloween, Los Angeles,” lead singer Gerard Way bellowed several songs in. “Did you guys think we were going to wear costumes or something? Brothers and sisters, we wear costumes every single day!”

That kind of posturing was hardly unexpected from a Goth-loving group widely considered to be the paragon of “screamo” -- that is, emo-core’s heavy metal cousin -- a black-clad unit that has appeared in countless magazine photos drenched in stage blood and whose discography is loaded with such song titles as “Cemetery Drive,” “Vampires Will Never Hurt You,” “The Ghost of You” and “Dead!”

But it also underscored the unusual solidarity of outsiderness the New Jersey group fosters -- something the British press recently vilified as a death cult advocating self-harm but that actually is closer in spirit to a support group for recovering social outcasts.

Its hypothetical motto might be Morrissey’s mope edict: “I wear black on the outside because black is how I feel on the inside.”

My Chemical Romance’s theatrically bombastic songs certainly worked a dark magic on the Halloween crowd, whipping it into a pogo-ing, pinkie-and-index-finger-waving, sing-along mass with messages of hope and redemption aimed at dejected, afflicted listeners who have a taste for guitars and eyeliner.

“They believe in the music they’re playing so much, it gives these kids something to believe in,” said fan Julie Kellman Reading of Los Feliz. “This band is speaking their language, which is why it all feels so poignant right now.”

Attendees gained entrance either by winning tickets in a KROQ-FM (106.7) giveaway or by standing in a massive line that snaked down Sunset Boulevard earlier in the day (the performance also was streamed live on the Web over AOL Music LIVE!). And many of My Chem’s faithful turned up in costume. An Ali G impersonator, a guy in a lab coat with a patch reading “Morgue Coroner,” a Johnny Knoxville look-alike, a “V for Vendetta” guy and a doppelganger for Misfits’ lead singer Glenn Danzig were seen among a sea of Southland youths in black outfits and kohl eyeliner.

Turns out that Allhallows Eve is also, fittingly enough, lead guitarist Frank Iero’s birthday and Way led the crowd in a rousing chorus of “Happy Birthday.”

My Chem drew most of the songs in its 75-minute set from its recently released new album “The Black Parade,” which has been generating critical praise and entered the Billboard album chart at No. 2 on Wednesday after selling 240,000 copies in its first week.

Among the emotional highlights of a performance in which the group proudly proclaimed its uncompromising emotionalism was an encore rendition of “Cancer,” a song from the new album in which Way slips into character as a withered chemo patient steeling himself for the journey into eternal sleep.

“I cried when I heard it,” said Lynda Rojas, 19, of Winchester, who was dressed as Harry Potter’s sidekick, Hermione Granger.

“People say this music makes you depressed, but it has the opposite effect. It’s happy and alive. It’s an uplifting experience,” said Rojas’ friend Traci Varalyay, 21, of Palmdale, dressed as a “dead cheerleader.”

Their friend Candice Odland, 21, of Riverside couched My Chemical Romance’s ability to provide musical catharsis in no uncertain terms.

“Seeing them, it’s almost like a religious experience,” she said. “You go to a different place for a while then you come back. And you’re better for it.”

chris.lee@latimes.com