"Yeah, I feel really good," the 27-year-old redhead told Letterman, who reminded her of his own battles with the bottle as a recovered alcoholic for nearly 30 years.
Letterman went through the motions, affecting a feminine voice, before revealing, "It's Dave, Oprah. It's Dave."
Watch the video on RadarOnline.com
The OWN boss replied, "Oh my god, very good, Dave! The David Letterman who’s retiring?"
Winfrey said she thinks the Mean Girls star is "doing okay.
"I think to have cameras following you around for every phase of your life and you’re trying to pull your life together, that’s a very difficult thing," the media magnate said. "We’re really pleased that she’s making some progress.”
Winfrey has "become a guiding light to me," Lohan said, and "been an amazing human being to me in my life."
The Late Show with David Letterman airs at 11:35/10:35c weeknights on CBS.