By Paul Robicheau

Saturday’s performance made up for a rain delay with the longest single set since the band’s millennium-greeting Everglades marathon.

Page McConnell and Trey Anastasio at Fenway Park. Photo: Paul Robicheau.

Each show tends to be completely different when you’re an improvisational rock band, especially one with the stylistic breadth of Phish, which ranges from goofy standard rockers to extended, abstract jams. Add a drenching thunderstorm like the one that delayed Saturday’s second of two nights for Phish at Fenway Park and you have a yin-and-yang scenario that only makes it more confusing to discern the headspace that drives both the band and its fervent following.

Unlike most classic-rock outfits (including Dead and Company), the Vermont-bred quartet has dipped into a well of new material this summer, including albums by side project Ghosts of the Forest and joke band Kasvot Växt. That fictional Scandinavian group, which Phish posed as last Halloween, suggests a jam-rock Spinal Tap. On Friday, “Say it To Me S.A.N.T.O.S” annoyed with its silly refrains of “This is what space smells like” and “Heigh ho! Heigh ho! Heigh ho!” Yet fans at Phish’s first Fenway show since the group returned from a five-year breakup in 2009 danced and shouted along, much as they continued with anthemic set-closer “Character Zero.”

Yes, Friday’s show came as close as Phish does to good-time stadium rock, easing into the fading sunlight with “Free” and the funky new strut “Blaze On,” where singer/guitarist Trey Anastasio sang “We’ll be dancing in the fields.” It was a scene far different from Connecticut’s Mohegan Sun Arena, where the group will play indoors this week to an exclusive crowd that’s one third the size. Action picked up in the second set with the cyclical groove of “Sand,” a bashing/lurching “Axilla” (pushed by Page McConnell’s organ) and the rising new suite “Mercury,” where drummer Jon Fishman dipped into a synth-marimba break. Phish also nailed the proggy “Fuego,” spouting absurdist lyrics about Viking warriors, Vlad the Impaler, and angels blowing horns. Granted, the band played well, even sounding surer than usual with multi-part harmonies. And the sound was excellent, aided by speaker towers spaced in a ring around the ball field. But Friday proved a light night tilted to standard frivolity, shortchanging the potential of Phish’s palette.

Phish at Fenway Park. Photo: Paul Robicheau.

Anticipation built for a flip-side burner on Saturday, even before thunderstorms flashed lighting and drenching rain that prompted a late opening of the park and the band to take the stage two hours after showtime. But it literally set up a day-and-night difference. Phish dispensed with its usual two-set format, emerging in shower-tempered darkness to bite into the nasty riff of “Carini” and kick off a 160-minute show that skipped intermission and blew 40 minutes past curfew.

The group displayed no immediate urgency, though slow funk vehicle “Wolfman’s Brother” surprisingly deconstructed into a soaring, guitar-spiked jam. And Phish continued to methodically work through its longest single set since a millennium-greeting Everglades marathon, throwing in elastic compositions as the blossoming “Reba” and rhythmically tricky rarity “Mound,” where Sudbury-bred Mike Gordon rode his meaty bass into the upper registers. “Down With Disease” stretched into a longer minor-key excursion, and the set reached a mighty culmination when a spotlight-whirling vamp on Deodato’s theme from 2001: A Space Odyssey dropped into a menacing “Split Open and Melt,” Anastasio’s dark tone dripping over the shifting time signatures.

Phish’s Mike Gordon at Fenway Park. Photo: Paul Robicheau.

A dynamic mid-set “About to Run” — from the guitarist’s Ghosts of the Forest, inspired by a close friend’s death — also injected serious pathos in Anastasio’s sober ruminations about desperation with Hendrix-ian guitar howls to match. By contrast, the refrain of later Kasvot Växt number “Death Don’t Hurt Very Long” seemed senseless, another in-joke to lighten the load along with the tequila-toasting ditty “Mexican Cousin” and sing-along oldie “Suzy Greenberg.”

Not generally a band given to socio-political commentary, Phish raised an olive branch for unity in the new “Rise/Come Together,” which opened the encore with Anastasio singing “We’re all looking for a little more love, to shine a light and lift us up.” But then “Wilson” — a rowdy number from the guitarist’s college thesis about a fantasy kingdom — came crashing in to cap the long evening, imploring “I must inquire, Wilson, can you still have fun?!” With glowsticks flying in the air instead of raindrops, the crowd heartily answered in the affirmative.

Paul Robicheau served as the contributing editor for music in The Improper Bostonian in addition to writing and photography for The Boston Globe, Rolling Stone and other publications.