The whole thing could have been vastly anticlimactic.

What initially had the look of the pop-culture event of the season -- megastar Britney Spears performing a free outdoor concert in one San Francisco's most storied and colorful neighborhoods -- certainly lost a bit of pizazz when the threat of bad weather forced organizers to move the show from the streets of the Castro district to inside the Bill Graham Civic Auditorium.

That Sunday's brief concert still managed to feel like a major event can be credited, almost entirely, to the enthusiasm of her fans.

They came from all over the Northern California, as well as across the nation and as far away as Europe, to see Spears tape a free concert for "Good Morning America." Her performance will be aired on the popular ABC-TV show on Tuesday morning, the same day her seventh studio album, "Femme Fatale," hits stores.

Tickets to the free, general admission show were released online in advance, but many fans began lining up at dawn in hopes of securing spots near the stage.

Alissa Jones was part of a group of six high school students from Walnut Creek and Danville who showed up at 7 a.m. They all wore buttons reading "Britney Spears is God."

"We are obsessed with Britney Spears," Jones said. "We want to get as close to her as possible."

Jones' friend Neda Hefzi says that part of Spears' appeal is that her career has had more ups and downs than a roller-coaster ride. She's a survivor.

"She's proof that you can be knocked down a thousand times and still get up," she said.

Camille Peyroulet and her five friends said they had traveled all the way from France to see the show. And Peyroulet said she had more than a passport stamp to prove her loyalty to the pop star.

"I have a Britney Spears tattoo," she said.

Once inside the venue, the 6,000-strong capacity crowd mostly waited for Spears to come on. The dead space was filled by five drag queens, who told jokes, talked about a planned after-party in the Castro and gave various Britney trivia bits.

Spears took the stage at just after noon to perform "Hold It Against Me," her No. 1 single from the new album, which boats digital sales exceeding 400,000. It's the fourth chart-topping single of Spears' career.

The production provided plenty of eye candy, with Spears gyrating about in a sparkly bodysuit while surrounded by six leather-clad male dancers on a darkly futuristic set. Whether the song featured any actual live vocal work was is highly in question.

That was followed by more waiting, as stagehands erected a new set for the next number, "Big Fat Bass," which also hails from "Femme Fatale." The tune lived up to its title, with a bass line so loud it rattled the fillings in your teeth. The production featured dancers in baggy, colorful outfits performing around giant speakers while a video of hip-hop star will.i.am (who performs on the album) was played on a large screen in the back.

Yet another set was erected for "Till the World Ends," a big, booming dance number that turned out to be the best -- and last -- offering of Spears' set. Afterward, Sam Champion and Robin Roberts of "Good Morning America" presented the entertainer with a certificate saying it was "Britney Spears day" in San Francisco. Whether that day was supposed to be Sunday or Tuesday wasn't immediately clear.

It might have been disappointing that Spears didn't deliver a few more tunes, given that some fans waited five hours or more to hear three songs. Yet, it would've been hard to find anybody in the crowd that thought the effort wasn't well worth it.