During day two of Life Is Beautiful, I followed live electronic act STS9 with Afropop-loving indie crew Vampire Weekend. Hardly an obvious doubleheader. The most the two have in common is a rock foundation to their respective, genreless aesthetics. As such, jumping from one to another within a 20-minute window would not feel natural to anyone but a seasoned festivalgoer, a reviewer or the most open-minded music fan. I hope anyone that dared to do so had as much fun and fulfillment as I did.

STS9, a Santa Cruz-based, improv-heavy quintet, got its start introducing the jam band community to electronic music, but didn't do so through DJ gigs or lining up synthesizers on stage. It incorporated keyboards and sequencers into its traditional guitar/bass/drums arrangement and, crudely put, gave Phish the Chemical Brothers treatment, minus the vocals and plus the occasional Parliament Funkadelic inspiration.

As evidenced last night, the electronic music element now dominates the sound, even when the guitar plays a more prominent part. It was there in opener "Kabuki," but it sounded as if it was playing singer to the dancefloor anthem beneath it, rather than charging up the audience—a responsibility that fell on the two percussionists, especially drummer Zach Velmer. That man would keep many a pair of feet happy for the set's hourlong entirety, pushing along an exhilarating, often building mix of synth waves, vacuum-like arpeggios, deep house grooves and disco-era riffs. It was an impressive musical execution, but it was hard to ponder the craftsmanship—or even the direction of any given song—with the escapism inherent to the numbers, especially the cosmic, layered "Scheme" and peak-hour epic "Inspire Strikes Back." Hands down my favorite set of the weekend.

A subsequent Vampire Weekend set exposed sharp contrasts: shorter songs, familiar song structures, jaunty rhythms, taut delivery, Afrophile fixations and, of course, the presence of vocals. And what a long way frontman Ezra Koenig has come from that first visit to Las Vegas, back in 2008 at the old Joint. Five years later, his poise before a much larger local crowd indicated a significantly matured performer, assured in his complicated fretwork and dynamic vocal projection. He often accomplished both at once, and he made it look easy.

Ditto for the entire quartet, actually. The performance of a song like the neoclassical ballad "Step" shouldn't come so naturally to a band known for its spunky impetuousness, but does, and it's as graceful as the song itself—one of a handful of songs Vampire Weekend played from this year's Modern Vampires of the City, itself further proof of the quartet's growth and comfort in its own skin. Another notable performance from that work, "Ya Hey," was twice as long—and satisfying—as most VW faves. Sure, breakneck nuggets like 2007's "A-Punk" and even this year's "Diane Young" offered the irresistible sugar spikes, but the real nourishment came from watching the group widen and deviate from the usual template.

Come to think of it, the compositional and emotional scope of "Ya Hey" swept me up in a way not too unlike some of the entrancing journeys STS9 concocted just an hour earlier. And who'd suspect they could have that in common?