Monday morning, past midnight, I should have been asleep. Instead, I was searching for the first song Jason Isbell and The 400 Unit played at Les Schwab Amphitheater hours earlier.

Granted, my job as a music writer entails a lot of this. I’ll spend a good chunk of time at any given concert scribbling fragments of lyrics in a notebook to furiously Google with the artist’s name later (yes, even if I’m a fan of the band — I’m notoriously bad at remembering song titles). This usually works, unless the artist in question has a predilection for lots of “yeahs” or “oh baby’s.”

What usually doesn’t happen is for these hastily scribbled lyrics to stick with me past the act of scribbling them. But that’s what kept happening Sunday night at Les Schwab’s 18th-season opener, a double-headliner featuring Isbell and eccentric alt-folkie Father John Misty that drew a crowd of roughly 3,200. (Opener Jade Bird dropped out due to illness, according to a post on her Twitter page.)

Isbell and his five-piece band (sans fiddler and Isbell’s wife, Amanda Shires) closed out the night, starting with the grinding, ascending riff that opens “Anxiety,” the 6-minute-plus centerpiece of the group’s Grammy-winning latest album, 2017’s “The Nashville Sound” — only here, The 400 Unit’s raw, rock ’n’ roll muscle replaced the recorded version’s crisp production. The riff built steadily before the band dropped out, leaving Isbell’s strummed electric guitar and voice for the first chorus. The haunting coda, “I’m wide awake and I’m in pain” — a perfect summation of anxiety disorder, delivered in an anguished cry to thousands of screaming, intoxicated fans — felt like a punch in the gut.

It wouldn’t be the last.

Nor was it the first. Father John Misty, aka singer-songwriter Josh Tillman, kicked the evening off a little after 7 p.m. backed by a massive nine-piece band that included a three-man horn section. The group created massive walls of sound for Father John Misty and the audience to get lost in, although it never lost the most important element — the songs themselves.

The enigmatic singer kicked things off with “Hangout at the Gallows” from his own new release, “God’s Favorite Customer,” posing a series of questions at the end: “What’s your politics? What’s your religion? What’s your intake, your reason for living?” Though less penetrable than Isbell’s words, Father John Misty’s lyrics delivered a range of emotions: “Mr. Tillman,” an early highlight, put the singer and his humorous observations on a psychologist’s couch (the Isbell name-drop naturally received huge cheers), while “Ballad of the Dying Man” later in the set was a somber lament to wasted time.

Perhaps the most affecting moment came on “The Palace” when the band dropped out almost entirely, leaving Father John Misty to serenade some loudly chirping birds (and audience members — at one point, he deadpanned, “I’m singing,” which managed to shut up most of the offenders).

The band rarely jammed, sticking to simple lines that serviced the songs while adding a serious dose of soulful funk to the folk-rock proceedings. That left Father John Misty as the focal point onstage, and he gladly took the spotlight, dancing frenetically when not holding a guitar. “I’m spontaneous — you never know what you’re gonna get, except all the dance moves,” he quipped at one point. “Those were all choreographed months ago, and I still f----- them up.” (That’s just one example of his self-aware banter. My other favorite: “This could be any one of my songs,” after the audience cheered for two strummed chords on acoustic guitar.)

Isbell may not have Father John Misty’s cult of personality, but he and The 400 Unit made up for it with deeply earnest performances — a seeming rarity in most modern, irony-obsessed, indie-alt-folk stuff — and sheer volume.

While Father John Misty’s band stuck to rock-solid arrangements, The 400 Unit got to stretch out more: Keyboardist Derry DeBorja took a number of standout organ solos throughout, while Isbell and guitarist Sadler Vaden traded snarling leads back and forth. And although the group needed no help, it got some from Isbell’s former Drive-By Truckers bandmate Patterson Hood, now a resident of Portland, during the two-song encore, which included an acrobatic workout on The Rolling Stones’ “Can’t You Hear Me Knocking” and the Truckers’ “Outfit.”

Isbell, like Father John Misty, often straddles the line between personal and political, as on the observational “White Man’s World” or new song “Overseas,” a lament for a ghost town where “the ghost got out.”

Again, though, one of the best moments came when the band cut out to almost nothing. The haunting “Elephant,” which featured Isbell’s acoustic guitar and voice backed by DeBorja’s subtle shading, relayed a story of a friend dying of cancer while she and the narrator “try to ignore the elephant somehow.”

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