Renée Fleming and Vanessa Williams sang together Saturday night under the roof of the Kennedy Center Opera House — the first indoor musical event at the nation’s performing arts showplace since the March 13 shutdown due to covid-19 precautions. And if the tightly safeguarded concert didn’t feel like business as usual, it did feel reassuringly like show business.

The stars were in luscious voice for “A Time to Sing,” an hour-long cabaret with a six-piece band during which the operatic soprano and actress-singer performed an eclectic program including songs by Sting, Stephen Sondheim, Benjamin Britten and Joni Mitchell. The production was live-streamed on the Kennedy Center’s On Stage platform. But the real breakthrough was a dimension that would not have been worth mentioning half a year ago: It was staged before a live audience.

Granted, the invited crowd would barely have filled a midsize college class: 42 guests, masked and seated socially distanced on the Opera House stage, having entered through the loading doors after temperature checks. The performers and musicians — subjected to daily testing for the coronavirus during a week of rehearsals — appeared on a platform situated between the spectators and the cavernous, otherwise empty auditorium.

With so many stages across the country idled indefinitely by fears of spreading the virus, this production felt miraculous. What made it possible, officials said in interviews before the event, was the size and configuration of the Opera House: its high-quality ventilation; the location of the loading doors, which backed up onto the arts center’s front plaza; and a design decision allowing ticket holders to walk unencumbered to their seats on the stage.

“I thought about flipping the relationship between the artists and the audience,” said Robert Van Leer, the center’s senior vice president for artistic planning. “We could bring the audience in that way, thereby minimizing the contact between the public and the building itself.” In consultation with the Cleveland Clinic and guidelines by the Centers for Disease Control and Prevention, officials developed dozens of safety protocols, covering everything from reducing capacity in restrooms to sterilizing makeup brushes.

The concert itself felt both intimate and grand — like a musicale staged in a living room with 2,364 vacant red seats. “Together tonight, I think we’re making history,” said Deborah F. Rutter, the Kennedy Center’s president. She welcomed the masked audience, seated on folding chairs arranged singly and in pairs, with a quote from President John F. Kennedy: “ ‘Every accomplishment starts with a decision to try.’ How appropriate for this occasion.”

For those who snared a paperless ticket — among them arts center board members and families of the stars, including Williams’s mother, Helen Williams — the evening crackled with some of the electricity that’s been stored for months on the nation’s dormant cultural circuitry. “It’s a joy singing for a live audience,” Fleming said, as the vocalists separately and together richly realized a song list of pop, classical and show tunes, assembled with musical director Rob Mathes. With the bill stocked with numbers such as Sondheim’s “No One Is Alone” and Hal David and Burt Bacharach’s “What the World Needs Now Is Love,” a spectator could not help noting a certain mission to console.

“Sometimes people leave you/ halfway through the wood,” the vivacious Williams sang, in a lyric from the Sondheim-James Lapine musical “Into the Woods.” Poignant echoes of the pain of a besieged nation reverberated again when Fleming delivered a captivating version of Harold Arlen and E.Y. Harburg’s “Over the Rainbow.” “When all the world is a hopeless jumble . . .” it begins.

The event did seem a bit otherworldly. Abiding by the District’s stricture that no more than 50 people gather, the arts center gave over the Opera House to a concert filled to only 2 percent of the auditorium’s capacity. As you made your way to your folding chair, bathed in the glow of rows of violet ceiling lights, there was the sense of crossing over to something familiar yet strange from memory — a bit, yes, like landing in Oz.

“It’s six months’ worth of ‘How do we do this?’ ” Rutter said in a phone interview before the concert. Experts told the arts center that efficient ventilation was crucial to maximizing safety. According to center officials, the audience area created for the concert on the Opera House stage experienced four complete replacements of air each hour. On the performance platform — separated from the audience by several dozen feet — the air change occurred five times an hour.

Fleming and Williams had been game from the get-go; in fact, they were ready to do the show in August, but the Kennedy Center decided that was too early. The singers had long been talking about collaborating on an evening of music, and were willing to undergo the safety measures. “We’re being tested every single day — we have that lovely nasal swab test,” Fleming said by phone last week. “What we did for love.”

The stars met through a mutual friend. The show was intended to cement their professional and personal partnership, and reveal some of their surprising shared backgrounds. Both grew up in Upstate New York, for example, and all of their parents were music teachers.

“We know each other as working moms who have a career on the side,” Williams joked in a separate phone call. Fleming put it this way: “We have been calling ourselves ‘the PTA crowd.’ ”

The concert showed off the vocalists’ range and ease with each other. Fleming did segue into classical, with renditions of Britten and William Butler Yeats’s “Salley Gardens” and Dvorak’s “Song to the Moon” and Williams sang her pop hit, “Save the Best for Last.” Fleming delivered a meltingly tender version of “So Big/So Small” from Benj Pasek and Justin Paul’s score for “Dear Evan Hansen.” Williams paid tribute to Lena Horne with a lush and torchy “Stormy Weather.” And they teamed up niftily for a debut song, “The Diva,” written for them by Andrew Lippa.

The one missing ingredient was the ovation this exquisitely healing experience deserved. The sound of 42 sets of hands energetically brought together did not come close to moving the needle on the applause meter. Even so, as a testament to artistry and tenacity, “A Time to Sing” itself was an exhilarating earful.