LAS VEGAS -- "Are there any '90s kids out there?" Demi Lovato asked coyly in the middle of her iHeartRadio Music Festival set on Friday night, teasing that she was going to bring out a special guest.

The screaming, sold-out Las Vegas crowd got a little louder. I could feel the anticipation around me as the people made some not-so-hushed guesses as to who the surprise might be. This was some straight-up Taylor Swift move, and Demi had control -- after all, she had dropped her new single, "Confident," hours earlier, and she must've been feeling pretty good.

When Demi introduced Stephan Jenkins, I saw a few phones whipped out, Wikipedia pages failing to load due to the festival-speed reception we were all getting. But when he started strumming his acoustic guitar, everyone realized they already knew the Third Eye Blind gold they were going to get.

"Wish you could step back from that ledge my friend," thousands of us sang in unison, every single person going nuts -- from the grey-haired gamblers to beanie-wearing teens who were unaccompanied for the first time.

Demi kept beaming. She had already opened her set with her feisty "Cool For The Summer," almost killed me with "Heart Attack," actually killed me with "Give Your Heart A Break," and she still had more to come. But as a '90s kids herself -- born 1992 -- she had to milk the moment with Jenkins as much as she could.

"This could be the peak moment of the night," Jenkins said during a break in "Jumper." He and Demi strutted down the stage's catwalk after he switched to electric guitar, high-fiving fans in the pit as they walked. And after a pause that was probably a little too prolonged, they launched into the chorus one last time.

Lovato, wearing three little buns on her head and a big, black, fluffy jacket, closed out with "Neon Lights."

Earlier that night, Sam Smith had brought out a guest as well. The U.K. singer invited collaborators Disclosure to the stage. "These guys changed my life," he said, launching into Caracal track "Omen," and then "Latch."

Shaggy was another surprise of the night. And after Demi's Third Eye Blind throwback, fans were definitely feeling the '90s jams Shaggy was doling out.

The iHeartRadio Music Festival closed out with Kanye West and continues Saturday (Sept. 19) with Jennifer Lopez, The Weeknd, Nick Jonas, Diplo, Fall Out Boy and Diddy, with whom Demi posed backstage on Friday night (along with performer Lil Wayne).