Lady Gaga's first Lollapalooza performance was on a small side stage in 2007, where she received more than a few bewildered stares and was unapologetically called a "trainwreck." So when she headlined the first night of this year's Lollapalooza, wearing the same silver-jeweled bra she wore at that first performance, she wasn't going to let anyone forget where she started.

"I had no record deal. No one believed in me," she said, tearing up. "But we did it. Thank you so much, from the bottom of my heart, for coming to this show tonight."

Photos: Lolla Day One | Seen & Overheard At Lolla Friday

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Earlier in the day, Gaga made a flashy cameo during a set by Monster Ball tour openers Semi-Precious Weapons, diving from the stage into the crowd twice wearing torn fishnets, denim shorts and hardly anything else, to the delight of her fans. When she wasn't singing, dancing, or soaking herself in blood during her own set, Gaga preached about her self-esteem struggles and her rough start in the music biz. "I didn't used to be brave," she said. "I was made fun of in school. I got told 'No,' but you have made me brave, little monsters. I'm gonna be brave for you."

Video: Lady Gaga at Lollapalooza

Her two-hour set was high drama and, unsurprisingly, not quite appropriate for the younger Gaga fans seated on their parents' shoulders, as she mused, "I don't know if you've heard, but I have a pretty tremendous dick -- so get your dicks out!" (Thankfully, no one seemed to oblige.)

After every couple of songs there was a costume change, but most of her ensembles didn't really follow any sort of pattern or theme: There was a lampshade-looking getup made of hair, a white nun's habit with a see-through rubber dress, and a green, shiny, Tinkerbell-esque outfit near the end -- as well as gushing blood, copious amounts of glitter and her infamous sparks-shooting bra.

Photos: Lady Gaga Fans at Lollapalooza

She played hits, including "Just Dance," "Telephone," "Paparrazzi," "Bad Romance" and "Boys Boys Boys," the latter dedicated to "my biggest fans, all the Chicago gays." As another nod to that first Lolla performance, Gaga explained that she and her DJ, Lady Starlight, used to have interludes of heavy metal music during her show, so she invited Starlight on stage to dance to Metallica's "Metal Militia," during which they also lit hairspray on fire.

While Gaga represented the flashier, glammed-up side of New York City, the Strokes took the other main stage back downtown for a no-frills set that proved that, despite laying low the past couple of years, this band really hasn't missed a beat. Though slightly distracted by the fireworks that went off during Gaga's show, a leather jacket-clad Julian Casablancas led the group through favorites like "Last Nite," "Juice Box" and "Reptilia." Even with little crowd banter, the chemistry among the band members was there.

Video: The Strokes at Lollapalooza

Earlier on, Chicago soul legend Mavis Staples -- in perfect form at 71 years old -- delivered inspiring gospel tunes in her low, powerful rasp, with help from her band and three backup singers. Staples started with cuts from her upcoming Anti- Records release, "You Are Not Alone" -- produced by another local hero, Jeff Tweedy of "the Wilco band," as she called them -- before Tweedy joined Staples on stage to play the record's country-blues title track.

While Staples provided old-school soul, Raphael Saadiq brought his retro soul to the other side of the park, where he got the crowd to dance and asked, "I want to ask you a question, Chicago: Do you love me?!" Saadiq also performed a snippet of "Feels Good," the hit song from Tony! Toni! Toné!, the group he was in before taking off with his solo career.

The rest of the day was heavy on synthesizer-driven dance music to gear up for Gaga. New wave heroes Devo put on one of the weirdest and most energetic sets of the day, complete with choreographed dance moves and a handful of costume changes. Blue and white energy dome hats peppered the crowd, as keyboardist Bob Mothersbaugh proclaimed, "Greetings, Chicago. It's 2010 and we're here to f*cking whip it again!," prompting most people to make whipping motions with their hands as the group played its best-known song.

Devo played tracks from this year's "Something for Everybody," the group's first LP in about 20 years. A highlight was "Don't Shoot (I'm A Man)," in which the members shout, "Don't tase me, bro!" The group started in gray suits with masks, then changed to black Devo T-shirts, followed by yellow one-piece jumpsuits, which band members ripped off of each other onstage to reveal the T-shirts again, along with shorts and kneepads.

Brooklyn indie-pop duo Matt & Kim followed Devo with the happiest hour of the day: Drummer Kim Schifino stood on her drums nearly as often as she played them, while keyboardist/vocalist Matt Johnson often had one hand on his synths while using the other to signal the crowd to get louder. They joked about Schifino's lack of cleavage and told the crowd about a dude who streaked through their show at Coachella. Teeth-baring grins never left their faces.

Along with fan favorites like "Lessons Learned" and "Yea Yeah," the couple covered parts of Biz Markie's "Just A Friend" and Alice DeeJay's "Better Off Alone," encouraged crowd surfing, and provided fans with balloons to blow up to create a rowdy early-evening dance party. At one point, Schifino stood on top of the crowd to do a quick booty dance (and then crowd-surfed), while Johnson climbed up the side of the stage structure.

The first time Matt & Kim played Lollapalooza, in 2007, it was at 11 a.m., and they drew a big enough crowd that when CSS couldn't make it later in the day, they were asked to play a second set. Their first Lolla experience might not have been a disaster, but like Gaga, they've sure come a long way, too.

Additiona reporting by Tye Comer and Jessica Letkemann