Asked who he'd like to see as president, O'Reilly dead-panned: "I'd have to say Clint Eastwood."
"Well why don't we ask him," said Stewart, mocking the Hollywood actor's widely panned speech in August at the Republican National Convention by getting out of his chair and staring at it while the crowd erupted in laughter.
In an apparent show of bipartisanship, Stewart even sat on O'Reilly's lap at one point. "And what would you like for Christmas, little boy?" O'Reilly said.
"The display that you saw tonight is why America is America. Robust, creative, no holds barred," O'Reilly told reporters after the debate.
Organizers said about 1,500 people attended the event, but the main audience was intended to be online, where the event was live-streamed for $4.95. On Twitter, viewers complained they missed the event when the video servers crashed. Organizers said video will be available for download and that those who experienced problems will be eligible for a refund.