How Chicago almost didn’t record #1 hit ‘If You Leave Me Now’

Chicago — the soft-rock gods who ruled the ’70s airwaves — almost left one of their definitive hits behind.

The year was 1976, the band was working on “Chicago X,” and then-lead singer and bassist Peter Cetera had this one track — “If You Leave Me Now” — he really believed in, even if everybody else needed convincing.

“[He] had a hard time getting that song on the album,” founding Chicago member Robert Lamm, 78, told The Post about the Cetera-penned tune that took the troupe of musicians in a radically different direction.

“We were rocking and jazzing, and then that song was the softest, most beautiful ballad that you could think of. It went No. 1 around the world, and we never could get over that [sound],” Lamm said.

“If You Leave Me Now” — the airy godmother of such signature Chicago ballads as “Baby, What a Big Surprise,” “You’re the Inspiration” and their second No. 1 single, 1982’s “Hard to Say I’m Sorry” —  will no doubt be on the set list when the Rock & Roll Hall of Fame band plays an intimate benefit for Musicians on Call at the Hard Rock Cafe in Times Square on Sunday. 

The charity — which dispatches live musicians to hospitals and other healthcare facilities — provides a sonic tonic for sick patients.

“The doctors and nurses noticed that the healing power of music helped everyone, no matter what kind of shape they were in,” Lee Loughnane, 76, who plays trumpet in the famous Chicago horn section, told The Post.

Loughnane, Lamm — on keyboards and vocals — and trombonist James Pankow are the three original members still with the now-10-man band, 56 years after it was formed in Chicago.

For them, it has indeed been a hard habit to break, despite a revolving door of musicians over the years.

“We show up every night — we know where all the bodies are buried,” said Loughnane with a laugh.

There’s a flicker of hope that Cetera — a founding member who left the group to pursue a solo career in 1985 — might return home to Chicago one day.

“You know, you never know,” Lamm said. “He lives kind of a private life. He recently retired for a while, but he may be coming out of retirement. It’s been a long time since we’ve had a long talk. I would love to, but so far it hasn’t happened.”

Still, Lamm said, anything’s possible.

“You might bump into somebody in the airport.”

In the meantime, they’ll be keeping up their busy touring schedule this summer — making local stops at Long Island’s NYCB Theatre at Westbury on June 23 and Catholic Health Amphitheater at Bald Hill in Farmingville on June 24, plus the State Theatre New Jersey in New Brunswick on June 25.

And, there is far more napping than partying on the road these days.

“Of course, for the first couple of decades, we were partying very hard and, you know, we had a good time,” said Lemm. “But it was time to put that away.” 

And they’re still not tired of playing timeless tunes such as the jazz-rock jam “25 or 6 to 4” or Loughnane’s fave “Beginnings,” from their 1969 debut album “Chicago Transit Authority” — which was the group’s original name before they shortened it to just Chicago.

“The songs have had an effect on different generations, and there was no way of knowing that until you get this far in life,” said Loughnane.

But Lamm’s heart belongs to a certain Chicago classic that he wrote.

“‘Saturday in the Park’ is a song that means a lot to me,” he says. “I grew up in Brooklyn, and whenever I would be in the city, I walked through [Central Park], and it brings back what it was like being a kid and then realizing that music was going to be part of my life.”

And having rocked from the ’70s into their 70s, they don’t care if being labeled ‘soft rock’ gives them a bad rap.

“In the beginning, they said we were more ‘experimental,’” said Loughnane. “But you can call it whatever you want.”