Brett Eldredge, Jerrod Niemann and Lee Brice perform at the 98.7 WMZQ I Heart Country Concert benefitting the American Heart Association at the Fillmore Silver Spring. (Kyle Gustafson/FOR THE WASHINGTON POST)

About 2,000 people crashed an intimate jam session Thursday night — at least, that’s what it felt like being in the audience at the Fillmore Silver Spring. Ditching the standard practice of performing one at a time, four country solo artists — Lee Brice, Jerrod Niemann, Brett Eldredge and Kelleigh Bannen — joined together for an off-the-cuff acoustic show.

The two-hour set was a fascinating mix of awkward improvisation and stellar performances from some of the fastest-rising stars in Nashville, with the added thrill of seeing the singers in an unrehearsed atmosphere. Even if the amount of whispering, side conversations and inside jokes among the singers made being a part of the crowd seem slightly intrusive, the extra-casual dynamic made for extremely entertaining viewing.

Brice, on a hot streak with back-to-back platinum singles and another speeding up the charts, served as the host for the event — which basically meant if there was a sudden stretch of silence, he reminded the singers whose turn it was to play.

Meanwhile, Brice and Niemann, close friends who have written many songs together, instantly took on the personas of the two cool older brothers. Eldredge had his role as the goofy younger brother, while Bannen became the sister that they all relentlessly tease.

“I guess we’re in Baltimore, technically,” Bannen started to say at one point, and the Silver Spring crowd loudly took offense to the statement. Bannen realized her mistake, and Brice egged on the audience to jeer louder.

Lee Brice and Kelleigh Bannen perform at the 98.7 WMZQ I Heart Country Concert benefitting the American Heart Association at the Fillmore Silver Spring in Silver Spring, MD. (Kyle Gustafson/FOR THE WASHINGTON POST)

But as soon as anyone started singing his or her own music, everyone went into supportive, collegial mode. Brice jumped in during Niemann’s groovy smash “Lover, Lover,” which usually requires many harmonies. And he sang along to “Only God Could Love You More,” Niemann’s latest tune, which the duo co-wrote (with pal Jon Stone) over barbecue on July 4. Brice also gave some encouraging shouts during Bannen’s “Oh My My,” and bounced along to her buzzy single “Sorry on the Rocks.” The others rocked out to Eldredge’s upbeat “Don’t Ya” and swayed when Brice crooned the first verse of uber-sweet “Love Like Crazy” and the emotional “I Drive Your Truck.”

The only potentially uncomfortable aspect of the show was that Brice was clearly the main draw. The audience sang-screamed along to all his songs, such as the gentle “A Woman Like You,” and it became difficult to hear him above the noise.

It was Bannen’s turn to play next, and she shook her head when Brice was finished. “You’re making me play my new song after you play your first Number 1?” she joked, right before launching into a tune she wrote last month.

Brice smiled. “Your new song is going to be your first Number 1,” he assured her.