Fans who filled the Saenger Theatre on Saturday night expecting comic Chris Rock got something else entirely: a raucous, raunchy, occasionally reflective and generally uproarious duo act featuring surprise co-headliner Dave Chappelle.

Chappelle actually spent more time onstage than Rock. After opening acts Eric Andre and Jeff Ross, and an intermission, the curtain parted to reveal an Old English “CR” logo on a video screen. But it wasn’t “CR” who walked out. It was “DC,” a drink, a smoke and a microphone in hand. As the realization rippled through the room, a standing ovation ensued.

Chappelle did four shows at the Saenger in February, as well as a “secret” late-night gig at the Bayou Barn on the West Bank. On Saturday, he and his pal concocted a last-minute, unscripted surprise of their own on the first of Rock’s three nights at the Saenger. In a sense, he was returning the favor from when Rock made a surprise appearance on a Chappelle-hosted "Saturday Night Live" show in November. 

Saturday's performance at the Saenger, Chappelle said early in the 20 or so minutes he did by himself, would be “a social experiment. Chris Rock is in Austin headlining my show. … What we’re trying to figure out is: Does it really make a difference?”

It did. Chappelle, whose cultural cachet has eclipsed Rock’s, was his unrepentant self. He solicited lighters to fire up cigarettes. Between long drags, he riffed on the Zika virus, Caitlyn Jenner and the Amish. He tried to tamp down the backlash over the Bill Cosby rape jokes he makes in a new Netflix special. “Coming after me for feminist issues is a waste of time,” he said, then cracked, “You know what the feminist movement needs? A male leader.”

Rock then sauntered out, dressed all in black, to his own ovation.

Cellphones were forbidden during the show. Attendees had been swept with metal detectors; any phones were secured in locked pouches. That no one could Instagram or Tweet the superstar comics’ summit delighted Rock: “Oh, you wish you had your phones, right?”

Rather than cede the stage to the man on the marquee, Chappelle hung around for an hour of back-and-forth.

They riffed on an obvious topic for any living comedian: “Did Trump do anything today?” Rock asked.

“No, he’s still languishing in that failure of a health care bill,” Chappelle replied, before adding, “I think Donald Trump is gonna save America by accident.”

Rock pondered how impossibly high Michael Jackson got on the anesthetic propofol. Chappelle sheepishly admitted, “I might have been that high.”

“I forgot who I was talking to,” Rock deadpanned.

“I get a little reckless,” Chappelle concluded.

They clearly enjoyed the give-and-take, rarely getting in each other’s way, but Chappelle seemed more comfortable with their spontaneous high-wire act. Thrown off his carefully constructed routine, Rock nervously contemplated a water bottle, unsure of where to go next. Addressing the audience, he noted, “Y’all got a weird show.”

Chappelle generally jumped in to redirect him. After Chappelle described his wife, who is of Asian descent, Rock responded, “But you still have a wife, Dave. I’m divorced.”

Rock’s divorce has supplied much fodder for his ongoing Total Blackout Tour. A funny comparison illustrated how much his ex-wife has profited.

Chappelle was eager to explore the divorce further. He placed a stool center-stage and invited his buddy to “talk it out.”

Edging toward the wings, laying back as a sort of droll, chain-smoking, anti-hype man, he questioned Rock: “How long have you been divorced?”

“I’ve been divorced for two glorious years."

When did he know the marriage was doomed?

“It’s an accumulation, man,” Rock responded. “I (screwed) up. I wasn’t a good husband.”

He confessed to cheating on his wife with three women while on a previous tour. In a moment of poetic justice, the 52-year-old discovered, while unsuccessfully hitting on Rihanna, that he’s no longer the cool young comic on the scene.

Onstage, Rock and Chappelle learned that each is a fan of porn star Alexis Texas. Rock described the destructive effect of his pornography addiction, how he got very specific in his taste for “an Asian girl with a black ass who speaks Spanish.”

“You’d love my wife,” Chappelle quipped, as Rock cracked up.

He recounted losing his house in the divorce. “Did your lawyer even try?” Chappelle asked.

It wasn’t all fun and games. After issuing a disclaimer that “this is a poignant moment,” Chappelle inquired about whether Rock cried at any point.

“Wow!” was Rock's reaction. But then he answered: Yes, during the custody battle over his kids, ages 15 and 13.

The room suddenly got very quiet. This was less comedy than therapy session. “You’re super-dad,” Chappelle said, offering support and reassurance. “You’ve been through the fire, bro.”

They found some humor, eventually, though Rock looked decidedly uncomfortable when Chappelle briefly returned to the rape theme. After a final bit about the hook-up app Tinder, Rock brought the show to an abrupt conclusion at 10 p.m.

It was ostensibly his night, but only Chappelle had done a solo set. Rock should have as well. With his guest onstage, he was never able to fully work himself into the exasperated cadence that is his signature, or flesh out his routines. Some fans may have felt short-changed.

But the comic mash-up, especially coming as a complete surprise, was its own reward. It would not be repeated at Rock's Sunday and Monday shows at the Saenger; Chappelle was kicking off his own five-night stand in Austin on Sunday.

“I just realized this might be one of the flyest things I’ve ever been a part of,” Chappelle said of the shared set. “The only thing better would be if Eddie Murphy lowered from the rafters.”

There was no Eddie Murphy. Rock and Chappelle were plenty.

Follow Keith Spera on Twitter, @KeithSpera.

Keith Spera writes about music, culture and his kids.