The band whose sound was so unique it was almost impossible to mimic called it quits at a sold- out show Saturday at the 1,100-person capacity Metro on Chicago’s North Side.

The finale quickly became one of the hottest tickets of the year, selling out in 20 minutes on October 21, with almost as many tickets bought outside of the continental United States as within.

Hundreds began lingering around the Metro days before the concert, hoping to somehow snag a ticket and get a last look at the band that has sold 17 million albums since its first, Gish, in 1991.

On Saturday night, the street in front of the club was filled with hundreds more hoping in vain to convince one of the lucky ones to part with a ticket.

Skipping an opening act, the Pumpkins, led by singer-songwriter Billy Corgan, opened with the powerful “Rocket,” establishing the tone for the first set and inspiring the audience to jump in unison and, of course, begin crowd surfing.

The Pumpkins broke the show into three sets, with the second – opening with the beautifully mournful “Muzzle” from the Mellon Collie and the Infinite Sadness album – featuring more introspective work, much of it from the band’s later albums.

The Pumpkins returned with a driving third set that again put the crowd in motion.

The band followed with three encores and literally sent the crowd home with more music – on a compact disc recording of the band’s first concert at the Metro on October 5, 1988. The CD is only 38 minutes long because that is all the material the band had compiled after guitarist James Iha met Corgan in a Polish bar on the city’s Northwest side earlier that year.

For more than a decade, the Smashing Pumpkins have somehow straddled the divide between artistic resolve and commercial success, almost implausibly refusing to allow one to dictate the other.

In the early 1990s, the Pumpkins emerged from the Chicago music scene, at odds with, yet closely parallel to the rise of the alternative rock scene out West.

While grunge groups from Seattle assumed the image of self-abusing slackers, the Pumpkins religiously honed their music with Corgan penning song after song.

Joe Shanahan, who owns the Metro, said Corgan compiled a huge catalog of material, sometimes writing five to six songs a week.

“They brought me a demo tape with four songs and it was like nothing else out there – it was heavy metal, goth, pop – and it all came from a tall, lanky, artsy guy whose voice was angelic and kind of like a banshee at the same time, a mellow Japanese guy on guitar and this hippie-type girl,” Shanahan said. “I told them if they could find a drummer, they could really make it in the Chicago scene. Pretty funny, huh?”

Shanahan said the band has been impossible to categorize. “They are a rarity,” said Shanahan, who sees just about every musical act on its way up through the Chicago scene. “Truly an original.”

The band continually kept fans and the music industry guessing, evolving with every album into an almost entirely new style.

And with their last album, Machina II: The Friends and Enemies of Modern Music, the Smashing Pumpkins shocked the industry again, releasing the album over the Internet free of charge as a gift to listeners.

Corgan at one point said to the audience, “Welcome, welcome, welcome … to the last gasp of the Smashing Pumpkins.”

Of course, Corgan was telling fans something they already knew. But many said they felt it was also the last gasp of a musical era.

Listeners can take heart, however. The prolific band recorded an unknown number of songs that never made it onto their half-dozen existing albums.