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The words "Imagine Dragons" were being muttered about several hours before pop rockers Walk The Moon hit the stage Saturday night, and it had nothing to do with any musical similarities.

No, there were concerns quietly bantering about that, two years after the breakout rock troupe pretty much broke Summerfest for a night with an absurdly packed crowd, a similar situation was brewing over at the U.S. Cellular Connection Stage with Walk The Moon. The stories sounded the same after all: In between getting booked for Summerfest and actually hitting the stage, both bands with a strong local contingent of fans (this marked the band’s fourth Summerfest trip) utterly exploded in popularity.

In the case of Walk The Moon, at just about the time the ground stage headliners were announced, its hit single "Shut Up And Dance" was in the process of graduating from fun poppy radio hit to world-destroying monster song of the year. Suddenly, their once reasonable ground stage digs seemed woefully insufficient.

Of course, those pre-show whispers and rumors ended up being slightly exaggerated. Summerfest seemed far from ever breaking last night. Summerfest red shirts seemed to have the show on lockdown, and ticket lines weren’t so insane that the Big Gig wound up letting people in for free, hopping turnstiles and turning the Summerfest grounds into a sweatily packed parking lot. It was certainly crowded, but it was also certainly livable.

Sorry, I said crowded when I meant to say CROWDED – all caps, all bold and in 72-point Impact font if possible. Early estimates placed the attendance for Walk The Moon at somewhere about 15,000 people – impressive considering the US Cellular Connection Stage only has a 8,000-person footprint of space. Impressive or horrifying; both adjectives work.

_{The view of the Walk The Moon concert from the Ferris Wheel. (Photo: FM 102/1)}

So Walk The Moon could clearly draw a packed house. The only question: Would they put on a show worthy of it?

Most certainly.

Triumphantly arriving on stage to the tune of "The Lion King," decked out with tribal face paint designs (or, you know, a nice rainbow in the case of lead singer Nicholas Petricca), Walk The Moon quickly erupted into the first of its many fizzy pop rock numbers, "Tightrope" – featuring a touch of the modern rock staple of pummeling the hell out of an extra drum. The rockers quickly followed that bright catchy tune with a pair – heck, really a whole set – of equally bright catchy tunes, "Next In Line" and "Sidekick."

Impressively, the songs managed to work despite what sounded like a fairly mushy audio mix. Petricca’s vocals often seemed slightly muffled – during "Next In Line," it almost sounded like he was in a phone booth from my location – and the bass often overtook the rest of the instruments on stage. The issues seemed to fade in and out over the course of the night. For instance, after "Sidekick," the mix seemed to come in a little cleaner for the vocal harmonies on "Down In The Dumps," as well as "Avalanche" … only to get drowned a bit by bass yet again on "Different Colors."

But, frankly, it was pretty much impossible to hold that against Walk The Moon. Petricca and company sold each song with fun, colorful energy – quite literally, as the pointing neon-lit arrows serving as the stage’s backdrop changed and shimmered different shades throughout the night. And if it was a touch hard to hear the vocals, there were 15,000 fans all seemingly singing along number after number after infectiously poppy number. From my location, the crowd did fine work making up for the mix. Thus is the benefit of having such hooky, sing-along-worthy tunes.

Petricca spent much of the show behind his glowing keyboard set, but he still exuded plenty of energy samba hip swaying and gyrating and generally bouncing around with a fervor, getting the crowd moving and involved. As for crowd interactions, his kind of life coach motivational speaker odes wore thin as the show went along (late in the set, he started "I Can Lift A Car" by basically leading the audience in a relaxation exercise). His more spur of the moment reactions and sentiments – "The view from up here is pretty f*cking awesome," for instance – seemed a little more real and less pre-packaged.

Still, Petricca had the crowd absolutely magnetized in the palm of his hand the entire show, so much so that when he asked the crowd to jump (which is the worst. Public service announcement to bands playing Summerfest: Most of the audience is standing on bleachers, so unless you want hundreds of snapped ankles on your conscience, stop requesting this) during "Jenny," the fans couldn’t say no despite their better judgment.

After "Different Colors," which Petricca opened with a nice statement about diversity and the Supreme Court’s recent ruling, Walk The Moon leapt into the rocking pop thrasher "Up 2 U" – complete with ’80s screamy guitar from Eli Maiman – and the particularly hooky "Portugal." Then it was off to "Aquaman," a Caribbean-dabbled ’80s/’90s throwback pop tune that would’ve made MJ proud, brought to a close with a strong solo from Maiman – a quiet MVP on the night with riffs cutting through the mix throughout.

"Lisa Baby" and "Jenny" were on deck next, followed by Petricca’s group meditation therapy and the rockingly aspirational "I Can Lift A Car," which got the whole crowd raising the roof – or invisible giant car in this case. It’s the kind of move that should’ve been a little dorky, but with Petricca and Walk The Moon’s addictive pop hooks leading the way, resistance was futile.

Of course, the finale was the band’s current mega-hit "Shut Up And Dance," which plays just as infectiously joyous and buoyant live as it does over the radio. The song sent the crowd wild, as well as the band’s opener MisterWives – who were egged onto the stage by Walk The Moon to join in the dance party. The band wasn’t done for long, however, as the crowd urged and earned an encore (as you would hopefully expect from a raucous, over-capacity crowd) coming in the form of Walk The Moon’s still crazy catchy first hit "Anna Sun."

And even though the chorus chimed, "This house is falling apart," Summerfest kept it together during the utterly mobbed evening. Fair to say if Walk The Moon comes back for a fifth Big Gig next year, they’ll be graduated to a bigger stage. And they’ll have earned it.