By Paul Robicheau

What could have simply passed for a nostalgic classic-rock spin turned out to be an expansive smorgasbord, frustratingly uneven at times, yet given to flashes of fervor and surprise.

Elvis Costello and the Imposters at the Pavilion. Photo Paul Robicheau.

The late ’70s intersection of punk and new wave yielded a broad, interesting range of musical styles beyond straight agit-rock — and two of the era’s most popular purveyors of that music split the bill on Tuesday at the now-named Rockland Trust Bank Pavilion. However, what could have simply passed for a nostalgic classic-rock spin through the hits for both British songsmith Elvis Costello and the New York outfit Blondie turned out to be an expansive smorgasbord, frustratingly uneven at times, yet given to flashes of fervor and surprise.

“You never know how things are going to turn out,” Blondie frontwoman Debbie Harry piped to the packed crowd at the waterfront tent after her band moseyed through a mid-set detour into rapper Lil Nas X’s recent No. 1 country-trap hit “Old Town Road.” But when she hit the stage with panache in a glittery riding helmet and mylar jacket to kick off Blondie’s opening 90-minute set with early hit “One Way or Another,” Harry showed little spunk or strength in her voice and one had to think the show might be a rough go. Granted, at a hard-to-believe 74, Harry’s only a year younger than Mick Jagger, so one might expect some drop-off in the vocal department.

On follow-up “Hanging on the Telephone” (another favorite from 1978 high-water mark Parallel Lines), Harry spoke through some of the lyrics, if to great effect, and Blondie built from there. They needed to boost the musical animation to match a barrage of imagery on three rear screens (women in “nasty” catsuits for “Doom or Destiny” and drag-club scenes for “Fun,” both from 2017’s Pollinator).

But when standout drummer Clem Burke doffed his white jacket to sport his black CBGB T-shirt and turn a brief solo into the driving, crackling disco beat of “Call Me,” Harry came to life as well, her ooohs escalating into full-bore vocals and fist pumps to the chorus. She continued to pick her spots and pace herself, settling into the casual rap phrasing of “Rapture” (whose strange style was once rejected, she told fans) yet giving her full vocal oomph in “Atomic,” which revved up the tempo near the end for an embarrassing if entertaining guitar romp by Tommy Kessler, who roved the wings, flicked picks to fans, and played behind his head.

Blondie today — (L-R) Chris Stein, Debbie Harry, and Clem Burke. Photo: Blondie’s website.

Seated original guitarist Chris Stein savored his chosen moments as well, evoking spaghetti-western lines in “Atomic” as well as thumb-picking deep, buzzing leads in “Rapture.” But the set’s main takeaway was Blondie’s stylistic wanderlust, from the Latin feel of “Wipe Off My Sweat” (Burke busting out timbale fills and Kessler switching to a mounted acoustic for flamenco turns), the humming guitar atmospheres of “Fade Away and Radiate,” and the island-flavored “The Tide is High.” Harry prompted fans to echo that song’s “Oh no!” punctuation, then bassist Leigh Foxx slipped into a familiar slinky line and Harry modestly sang “Groove is in the Heart,” the 1990 club/dance hit by Deee-Lite. Similarly, she tacked Donna Summers’ “I Feel Love” at the end of “Heart of Glass.” Add a couple of keytar turns by Matt Katz-Bohen to boost ’80s flashbacks and all of Blondie’s old and new members were spotlighted, although Burke’s flamboyant pulse helped keep the group’s danceable showmanship both alive and grounded.

Elvis Costello had his own troubles at the very start of his 90-minute whirl when “Pump It Up” fell prey to static in the sound system. But Costello, 64, was the one who was pumped up, clearly putting last year’s surgery to remove a malignant tumor behind him, giving a busy touring slate with the Imposters (essentially his old Attractions with new bassist Davey Faragher). Costello played his guitar with a flourish, raising arms to exhort the crowd in his opening run of oldies “Miracle Man,” “Clubland” (with Steve Nieve tinkling away on grand piano) and – without following through on a threat to cover Justin Bieber — “Accidents Will Happen.”

Costello’s band wielded more punch (due in part to the super-solid Pete Thomas’ loudly mixed pop on the drums) than their show at the Boch Wang Theatre last fall, when much of the set was devoted to their fine, stylish new album Look Now. But Costello slowed things down to inject two of those songs at the Pavilion, the haltingly crooned “Photographs Can Lie” (about a young woman’s cheating father, teased with “The Look of Love” in a nod to collaborator Burt Bacharach) and the lesser, more pedestrian “Mr. and Mrs. Hush.” Then the band returned to vintage fare with a booming “Beyond Belief” dropping into the sinuous reggae groove of a tour-de-force “Watching the Detectives,” Costello digging in with a menacing vocal and lashing, atonal guitar while movie posters flashed on the screens.

With backup singers Kitten Karoi and Briana Lee joining him front, Costello lent rambling thoughts on songs that Elvis Presley might sing today before a take on Sam and Dave’s soulful “I Can’t Stand Up for Falling Down” and his own nugget “High Fidelity.” They lent delightful vocal counterpoint to a bouncy “Everyday I Write the Book,” which stretched into a too-long band introduction, before saved with a tagged-on “Alison” that began with Costello singing alone over light chords. Alas, since his catalog’s more sprawling than Blondie’s, the rambling asides took away chances to tuck a couple more classics into a seemingly short 90 minutes.

Elvis Costello and the Imposters at the Pavilion. Photo: Paul Robicheau.

“Will you still love, a man out of time,” Costello sang in an encore that closed with a blast through “Radio Radio” (which he famously ripped into against orders on “Saturday Night Live” in 1977 and was banned on the show for 12 years) and Nick Lowe’s “(What’s So Funny ’Bout) Peace, Love and Understanding?” In turn, his shows’ usual good-hearted finale was accented with a more-than-usual political bent. On the backdrop, imagery urged the crowd not to join the military, an American flag was overlapped by a sickle, and quotes declared “Thou shall not kill” and “Stop adoration of the warrior class.” It was a pointed, sobering insertion that broke the happy nostalgia balloon, adding food for thought on a night that mixed fun with a sometimes surprising edge from two bands that shared – and share – an era.

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.