We had Las Vegas' MGM Grand Garden Arena covered for the fest's fifth-year anniversary, from the audience to the press room to our backstage video and photo lounge and everywhere in between.
iHeartRadio Music Festival Day 1: 41 Things You Need to See
Check out all the things you might not have seen during the jam-packed first day, from Demi dancing to Diplo:
5:23 p.m.: The best way to start day 2 of the fest: Overhearing Hozier sound-checking "Take Me to Church."
5:57 p.m.: George Ezra tells reporters in the press room the difference between performing at festivals last year versus this year. "I play just as many shows; now there's just people coming to them," he joked. His biggest accomplishment? Playing Glastonbury. "I wanted to high-five myself when I got offstage, just because I'd done it."
6:48 p.m.: Alvaro Soler had a hit on his hands with "El Mismo Sol" -- and then one email launched it into another stratosphere. "I already thought it was going really great, and then we heard from Jennifer Lopez," he marvels to reporters.
6:54 p.m.: Tove Lo had already played the iHeartRadio Music Festival Daytime Village when she hit the press room, so she explains her plan to change it up for her main-stage set. The daytime fest was "playful" while nighttime would be "dark" and "emotional."
6:57 p.m.: Zella Day tells reporters backstage that the moment she knew she "made it" was when she played the Daytime Village's rotating stage on Saturday afternoon. "I'm on a revolving stage and this is very rock-star," she recalls thinking.
7:24 p.m.: James Bay got very comfortable in the press room (see the photos below) and even complimented one reporter's query about his jam session with the Rolling Stones' Keith Richards on his way out the door. "Great question about Keith. Nailed it!"
7:47 p.m.: The Weeknd kicks off the show with "Losers," from his No. 1 album Beauty Behind the Madness. He makes a slight tweak to the lyrics to get the crowd energized during the downtempo track: "So what can you show me, Las Vegas, now my heart don't know already."
7:55 p.m.: For his sultry Fifty Shades of Grey hit "Earned It," The Weeknd enlists the crowd's help. "Sing that shit, Las Veags -- let's go."
8:03 p.m.: After "Can't Feel My Face," The Weeknd assures fans that it's not over as the blasting intro of "The Hills" kicks in.
8:07 p.m.: Wilmer Valderrama -- on hand to support girlfriend Demi Lovato and promote his new Fox show Minority Report -- talks about secret dinners with his That '70s Show castmates. "It's like riding a bike," he tells reporters of reuniting with the cast. "We go right back to giving each other a lot of shit."
8:12 p.m.: Shawn Mendes tells the press room that he honestly believes that Justin Bieber didn't know who he was. "The 'shade' was probably blown out of proportion."
8:18 p.m.: Jennifer Lopez promises a few surprises for the night, and after bringing out Soler for "El Mismo Sol" (their first performance of the song), she reveals the artwork and title of her upcoming Las Vegas residency: "All I Have."
8:21 p.m.: Lovato and Valderrama join on/off J.Lo boyfriend and backup dancer Casper Smart in a VIP section to watch the Latin superstar light the stage up with "On the Floor" and "Jenny From the Block" -- and do some dancing themselves.
8:32 p.m.: "What I learned from Prince was: Just make good music," actress/singer Kat Graham tells reporters of working with the legend on her upcoming album.
8:45 p.m.: Blake Shelton got a little nervous when he found out he was following J.Lo in the lineup. "What the eff? What am I doing here?" he jokes, before warning, "When I get nervous, I tend to drink a little bit, OK? I'm just being honest with you!" He then, appropriately, launches into "Sangria."
8:59 p.m.: After "Boys 'Round Here," Shelton leaves the stage with a red Solo cup in the air.
9:03 p.m.: Prince Royce kicks off his set with "Stuck on a Feeling," his biggest English-language song to date -- even adding a little extra flair to Snoop Dogg's verse by playing it over the "Drop It Like It's Hot" beat.
9:08 p.m.: Vampire Diaries actor and singer Michael Malarkey had a fitting explanation for why Kanye West was barely visible during his Friday night set, likening his darkly lit stage to the Gorillaz cartoon live show. "It's not about him; it's about what he's doing," he tells reporters. He also drops some hints about his sophomore EP Knots, due Nov. 20, which is inspired by Nick Cave and Leonard Cohen.
9:15 p.m.: When Prince Royce sings his ballad "Lucky One," it turns out the real lucky one is the fan he plucks from the audience. The Latin heartthrob serenades the young fan, complete with a single red rose and countless hugs.
9:23 p.m.: Prince Royce takes a page from Jason Derulo's playbook and loses his shirt during his closing number, "Back It Up." Fans might have expected J.Lo to make an appearance, since she's featured on the song, but his fellow iHeartRadio performer is already making the press rounds following her bombastic set.
9:32 p.m.: While Big Sean censors himself for "I Don't F--- With You," the crowd doesn't. Good luck to the CW censors with that one! Unexpectedly, that's the only song Sean is allotted to perform.
9:44 p.m.: Echosmith's Sydney Sierota got the chance to hit the stage with Taylor Swift for a second time on the 1989 World Tour "was like hanging out with a good friend -- in front of thousands of people."
9:49 p.m.: G-Eazy tells reporters about getting the chance to have dinner with Jay Z. "I could have climbed a mountain that night -- or beat Kobe at basketball," he says.
9:53 p.m.: Hozier, naturally, closes with the massive hit "Take Me to Church," following a set filled with mood lighting and rich strings.
9:56 p.m.: It was Lee Brice's sound guy that gave him the idea to hit all 50 states on his 2015 tour. "He says to me, 'You know, we're only seven states short.'" And with Alaska and Hawaii already under his belt, it only made sense for the Daytime Village performer to tack another eight dates onto the (already-packed) tour to meet the goal.
10:19 p.m.: OK, Jason Derulo officially started something. Now Trey Songz is losing his shirt to close out his set with "Bottoms Up." Way to be a trend-setter, Jason.
10:33 p.m.: "Let's talk some bodies." -- How Tove Lo introduces "Talkin' Bodies"
11:07 p.m.: We asked for another Bad Boy reunion, and we got our wish. Puff Daddy kicks off his collab-heavy set with Mase and "Bad Boy for Life." "I was supposed to leave tomorrow; [now] I'm staying until Wednesday," Puff tells the Vegas crowd. "I'm inviting all y'all to a party -- drinks on me. Let's rage till Wednesday!"
11:09 p.m.: Busta Rhymes is up next, for "Pass the Courvoisier" -- oh wait, scratch that. Liquor mogul Puff changes the chorus to "Pass the Ciroc This Way."
11:16 p.m.: Machine Gun Kelly is the next guest, starting with his own song before -- yes -- removing his shirt (that's three ab-tastic performances in one day!) for "All About the Benjamins." Lil'Kim also hits the stage for a single verse, introduced by Puff as "the queen of hip-hop."
11:29 p.m.: Just when you thought there were no more guests, Diddy-Dirty Money's "Coming Home" kicks in, and Tori Kelly comes out to wail the chorus. She did such a good job that Diddy fell down onstage with her powerful final note.
11:50 p.m.: Nick Jonas takes a break from his funky track "Teacher" for a seamless interlude of Bell Biv DeVoe's "Poison." He also shakes up his biggest hit, slowing down "Jealous" with a very Prince-like electric-guitar intro.
12:01 a.m.: After playing "Sugar, We're Goin Down," "Uma Thurman" and more of their hits, Fall Out Boy welcomes Fetty Wap to sing his megahit "Trap Queen," reprising their April performance at the MTV Movie Awards.
12:41 a.m.: Diplo lights up the Garden Arena stage in his closing set, bringing out singer/songwriter Priscilla (Fifth Harmony's "Worth It") to sing "Be Right There," his collaboration with Sleepy Tom. As concertgoers file out into the lobby, the smoke from Diplo's pyro is still hanging thick in the air.