The plan was simple: Justin Bieber would play two acoustic songs in the middle of his set, then hand off his guitar and get back to the programmed dance music.
But when a stagehand approached the young pop singer following a rendition of his song "Love Yourself," Bieber casually waved him off. Clearly reluctant to give up the instrument, he instead launched into Tracy Chapman's "Fast Car," of all things, murmuring breathily as he plucked out the folk tune's distinctive riff.
The thumping club beats would have to wait.
Bieber's unexpected coffee-shop moment was one of many instances of old-fashioned musicianship at Jingle Ball, the annual all-star Christmastime concert put on by Los Angeles' powerful Top 40 radio station, KIIS-FM (102.7).
It's an event that typically showcases other skills: the ability to execute choreography while wearing a Santa hat, for example, or to thank a program director without making it sound like a professional obligation.
Yet this year's edition — held Friday night at Staples Center, where the bill also included Bruno Mars, Britney Spears and Niall Horan — felt crowded with artists eager to flex their chops.
First among those was Bruno Mars, who opened the four-hour show with a quick but vivid sprint through some of his biggest hits.
Mars learned to play as a member of a family band that performed in hotels in Honolulu, and he's never shaken his attachment to old-school razzle-dazzle. Here was a guy who had a vintage dance step to go with every throwback texture in songs like the James Brown-ish "Runaway Baby" and "24K Magic," a pitch-perfect homage to early '80s funk.
But Mars also maintains the lifer's determination to keep himself amused, which is why he and his band kept adding fresh touches to familiar music: a new horn lick in "Treasure," churchy organ to accompany "When I Was Your Man," subtle harmonic and rhythmic variations in "Uptown Funk" that told you these were real players working in real time.
And if none of the screaming kids in the arena noticed (or cared?), no matter. Mars knew.
Even bigger screams broke out when Horan sauntered onstage — an indication that for this member of the boy band One Direction, which is currently on hiatus, how he sounded at Jingle Ball was less important than how he looked.
Yet Horan took his time performing the rootsy "This Town," his debut solo single, feeling its gentle melody and finger-picked guitar part in a way he rarely got the chance to do in One Direction.
More musicianly moves came from Alessia Cara, who dug deep into her moody R&B ballad "Here," and Lukas Graham, the Danish combo that delivered its crafty soul-rock songs with the earnest determination of a high school jazz band.
Not every act wanted to be seen as some kind of virtuoso.
In a cursory DJ set, Diplo seemed most concerned with getting people in the crowd to do jumping jacks. And though Britney Spears danced well, her physical performance came at the cost of live vocals; she appeared to lip-sync everything except for "Slumber Party," for which she was joined by Tinashe.
No wonder KIIS had promoted Spears' performance with the fact that Friday was her birthday rather than by talking up "Glory," the strong comeback album she released a few months ago.
After the station's crew presented Spears with a cake, Bieber emerged to the evening's loudest shrieks to finish the night. And at first, as he sang along distractedly to "Where Are U Now" and "Company" — both blaring from Staples' sound system in prerecorded form — it seemed his heart wasn't in the effort.
"I just got back from tour," he said, adding that he'd played more than 100 shows and was "pretty beat."
But then he grabbed that guitar and did a stripped-down rendition of "Cold Water." Visibly buoyed, he followed that with "Love Yourself," which he'd cleverly transposed to a minor key. Now Bieber was getting into it.
"Should I bring it an octave higher?" he asked, and of course, the crowd roared back in the affirmative.
But you understood the octave wasn't important. This teen idol just wanted a few more minutes to be a troubadour.