Imagine wandering into a late-night downtown jazz club, ordering a drink and gazing at the tiny stage as the band members finish their warm-up. The singer quietly enters, adjusts her microphone and the announcer welcomes the crowd.

“Say hello to Miss Renée Fleming!” A smattering of applause as she launches into “Just One of Those Things.”

Hey, it could’ve happened. We’ll let the world-famous opera singer explain. She returns to Boettcher Hall for a one-night engagement with the Colorado Symphony on Saturday, by the way.

“It wasn’t all opera,” she said of the birth of her long career. “When I was young, I played guitar and piano, and when I was in college at Potsdam State (in way upstate New York) I was in a jazz group. Later on I realized that I got my head in way above water.”

With a little research, we discovered that Fleming had spent some of her collegiate weekends partnering with a pianist named Larry Ham in a jazz trio at an off-campus pub. One day, the famous tenor sax player Illinois Jacquet led a master class at Potsdam and apparently was quite impressed with young Ms. Fleming, and a lengthy series of talks about a recording project began.

That college meeting with a real live jazz professional proved a turning point, the soprano recalled.

“It was getting serious,” she said. “But I just didn’t see myself going in that direction. (Jacquet) wanted to go on tour. I decided, no.”

But as it turned out, that was not the end.

Flash forward to December 2003, when Ham, Jacquet and Fleming met again for a one-shot studio performance at WNYC — offering songs by Jobim, Gershwin and Duke Ellington. (Jacquet died the following year.)

Fleming is now 64 and showing no signs of slowing down in the world of staged opera and the concert hall, where she comfortably dips into her vast songbook of Broadway, light classics and contemporary pop. If her devoted fans stick around at encore time, you never know what she might have up her sleeve. Surprises are part of the singer’s calling card. That’s old news for those who’ve followed her career whether on the stage or on screen, where she recently starred in two IMAX travelogue-style visits to Paris and Venice, and is currently collaborating with National Geographic on a documentary titled “Voice of Nature.”

Nothing too unexpected for this well-traveled, and perpetually modest international star.

“Either you change or you don’t,” she said, adding with a chuckle, “I always wondered what it would be like to be a diva. But I guess that will never happen. I’m just me.”

She is simply someone who loves trying a little bit of everything and seeing if she can do it.

“I like having that variety,” she said. “It’s nice to provide a spectrum.”

That spectrum at the Boettcher concert includes “Twilight and Shadow” from the “Lord of the Rings” soundtrack by Howard Shore.

“My daughter asked for that.”

There will be other treats on the printed program, including two excerpts from the song cycle “Winter Morning Walks,” a collaboration by soprano Dawn Upshaw and Maria Schneider, the much-acclaimed composer and leader of a jazz orchestra (Ah-ha! Jazz – There’s that word again).

Opera lovers will not be disappointed, even if the program also includes songs by Icelandic songstress Björk (“All is Full of Love”) and the a-cappella classic “Pretty Bird” by mountain-music immortal Hazel Dickens. The evening also includes opera arias by Handel, Leoncavallo and, of course, Puccini.

“I’m guided by my own musical and intellectual curiosity,” Fleming said. “I choose not to be limited.”

Speaking of unlimited, she has not retired from the opera stage just yet. She’ll return to the Met next spring to star in Kevin Puts’ “The Hours” (His song “Evening” is on her Boettcher program), and she’ll travel to Paris for John Adams’ “Nixon in China” in the coming season. Plus the occasional cameo roles to be announced.

As for the challenges of singing in Boettcher Hall, the soprano should not be bothered by the room’s vastness and roundness: She’ll be resorting to a microphone when necessary.

“It’s about 80 percent classical,” she said of the program.

Still, that would seem to present some vocal problems.

“Yes, there’s a stylistic shift in a concert like this. I’ll get all that (voice) musculature worked out. And I’ll make sure the sound engineer makes the adjustments with the microphone.”

If anyone knows how to work a mic, it’s a former jazz chanteuse.