The mark of a true superstar musician is not when your fans sing a chorus or two, but the whole song.

On Saturday, Oct. 23, Chaka Khan turned over singing duties on her No. 1 classic “Sweet Thing” to fans, who sang verse and chorus as if they were oxygen. Yes, the legendary singer gave an assist here and there to keep the tune moving — especially as she famously delivers the high notes that are a torture test on the vocal chords — but it was the audience that proved the song was as much theirs as it was Khan’s.

After five decades of workmanship, Khan, with the help of opening act Freddie Jackson, proved during her roughly 85-minute performance at the Stockbridge Amphitheater that there is nothing like experience.

Khan, if you closed your eyes, sounded as good Saturday as she would have back in the ‘70s with the band Rufus, when they hit with disco-inspired “Once You Get Started.” Sure, eyes opened, you realized the audience was a lot grayer, and Khan’s stride was slower, but those pipes were remarkably strong.

“That’s my first great-grandson,” Khan, 68, said pointing to toddler Mackenzie, who was born in 2019. “And he’s from right here in Georgia.”

Credit: Daniel Varnado

Credit: Daniel Varnado

Khan, dressed in a two-piece outfit that shimmered purple in the stage lights, at one point took a short intermission while the band played “And the Melody Still Lingers On.” The 1981 tune is a tribute to jazz greats Dizzy Gillespie, Charlie Bird and Miles Davis using “Night in Tunisia” as the track’s melody.

Opening with “This is My Night,” Khan, her trademark raven hair blowing, told the crowd a lot of the evening would be dedicated to her Rufus days. That led to two of the group’s top 10s — the funky, slow burner “Tell Me Something Good,” written by Stevie Wonder, and the uptempo “Do You Love What You Feel,” which featured that insistent whistle-double clap combination that was popular in the ‘70s.

“Everlasting Love” and “Hollywood” from Rufus’ 1977 album “Ask Rufus,” worked as warm-ups for “What Cha’ Gonna Do For Me” and the night’s main events — the girl-powered “I’m Every Woman” and the Prince-penned “I Feel For You,” whose scratch opening “Chak-Chak-Chak-Chak-Chaka Khan, Chaka Khan” made Khan a household name.

“Ladies, this song is for you,” Khan said before the opening swirl of violins that are a hallmark of “I’m Every Woman.”

She closed with “Ain’t Nobody,” her last No. 1 with Rufus, which became one of the band’s biggest hits during concert performances as they were breaking up.

Not to be outdone, the playful and chatty Freddie Jackson, dressed in a brocade cream suit with yellow highlights, opened the night with “Nice ‘n Slow” and “Have You Ever Loved Somebody.” The two mid-’80s, mid-tempo numbers set a smooth pace for the night.

Credit: Daniel Varnado

Credit: Daniel Varnado

As with Khan, Jackson’s vocals seemed undiminished by time. His voice was both strong and engaging as he demonstrated the R&B crooning missing from today’s hip-hop-dominated charts on “I Could Use a Little Love Right Now” and “I Don’t Want to Lose Your Love.”

He teased about his friendship with the late great Luther Vandross, whom he was often pitted against as a rival because of their similar musical styles. In reality, he said, they were great friends, with Jackson mimicking Vandross’ signature vocal inflections and flourishes.

Like Khan, he saved some of his best for last, getting concertgoers on their feet for “Jam Tonight” and “You Are My Lady,” which has become a perennial love song at Black weddings (rivaled by Vandross’s “Here and Now”).

Credit: Daniel Varnado

Credit: Daniel Varnado

By the time he unveiled “Rock Me Tonight (For Old Times Sake)” as his closing number, the audience was ready to sing every word with him as they would later in the evening for Khan on “Sweet Thing.”