"We have a couple of options," he said. "We can say goodnight now and you can get a refund and go home, or I can stay out here and think of something to do."
Not surprisingly, the crowd went nuts for the second choice, and a determined Osmond ad-libbed his way through about 25 minutes, at which point Marie unexpectedly showed up during a dance routine.
Although she could barely croak out sounds, she too gave it her best shot, handling the choreography well but playing down her vocals. The audience loved it, perhaps even more than they would have with the scripted performance.
Donny Osmond didn't hesitate to brag about his philosophical inheritance when I reminded him of that night during a recent phone call.
"I don't see [that old-school effort] at all anymore," he said. "It's like everybody hides behind production. And, you know, people don't walk out of a show humming the lights, or the sets.
“What kind of personality did you leave them? What kind of songs did you leave them? That's what's important."
That, he explained, is what he learned from the many show-biz immortals he and his family worked with when he was a kid in the 1960s and '70s.
"Show business is a lot more than throwing a lot of production out there," he insisted. "I come from the school of [Frank] Sinatra, Sammy [Davis Jr.], Dean [Martin], Andy Williams, Jerry Lewis. I was a little-bitty kid learning from Lucille Ball and all these kinds of people [who] came from vaudeville.
“If you had a broken light or sound system, you did the show because people paid to see you do a show. And I think people walked away with a better appreciation because you did."
There is one aspect of old-time show business that Osmond, 54, reluctantly has ceded to the ash heap of history: the television variety show.
Although some of the most popular contemporary programs — competition series like "Dancing With the Stars," "American Idol" and "America's Got Talent" — recall the golden age of the variety show, Osmond is certain today's audiences wouldn't make it through the kind of extended segments that punctuated "Donny & Marie," the Osmonds' weekly series.
"I thought a lot about it. It's just not gonna work the way the ‘Donny & Marie' show worked back in the '70s," he offered. "The bar has been raised, but the bar has been changed. Variety is different. People expect so much more.
“If you put the ‘Donny & Marie' show up against ‘America's Got Talent' or ‘American Idol,' it probably wouldn't hold up. We are now in the mentality of a 60-second performer. We're living in a YouTube world: ‘Gimme a 60-second clip.' That's what's frustrating.
“But it's the world we live in. So deal with it, you know? I don't think we'll ever see [classic variety-style TV] in the same way it was back in the '70s."
As for this week's Caesars program, it is identical to the Flamingo presentation — lock, stock and barrel. According to Osmond, currently preparing to record what will be his 60th album (and also preparing for the arrival of his fifth grandchild), that was the only way he would have consented to perform in Atlantic City.
Caesars Entertainment Eastern Division President "Don Marrandino has been asking me to get out there," he said. "And I said, ‘Don, we have worked so hard to polish this show out here in Vegas. Anything less than what we have here [won't suffice].'
“He said, ‘Then replicate it.' I said, ‘You're talking about the dancers. You're talking about our costumes. You're talking about everything.' He said, ‘I don't care. Bring it out!' So we're bringing everything."
Caesars Atlantic City, Boardwalk at Arkansas Avenue, 9 p.m. Tuesday through Friday, 2 and 9 p.m. Saturday, 2 p.m. Sunday, $120-$50, 800-736-1420, ticketmaster.com.
Contact Chuck Darrow at 215-313-3134 or firstname.lastname@example.org. Follow him on Twitter @chuckdarrow and read his blog philly.com/casinotes.