The musical reunion, which featured Schwartz accompanying Chenoweth on the piano, was part of the Oct. 26 Dramatists Guild Fund Gala, Great Writers Thank Their Lucky Stars.
Prior to their performance, Schwartz opened up to Playbill.com about the "enormous influence" Chenoweth had on the creation of the long-running show and his reaction to the new "Out of Oz" music video series.
"She was involved with Wicked for about three years before we even went out of town," Schwartz recalled. "She did our very first full reading of the show because she happened to be in L.A., and I knew the person she was staying with and I invited her."
"As soon as Winnie Holzman and I heard her read and sing the part of Glinda, we thought, 'Oh, we have to have her do this.' "Consequently, both in terms of the writing of the role and some specific things that I wrote musically that hadn't yet been composed, when Kristin joined us, they were really written for her," he continued. "She had enormous influence on the creation of that show."
Wicked opened at the Gershwin Theatre Oct. 30, 2003, and the record-breaking hit musical celebrates its 5,000th performance on Broadway Oct. 28. It will also mark its 12th Broadway anniversary this weekend.
See Chenoweth and Schwartz performing at the gala in the video below:
Schwartz also commented on the recently released video of Aaron Tveit and Rachel Tucker singing a stripped-down version of "Defying Gravity," the first in a series of reimagined songs from Wicked. The songs were released as part of the "Out of Oz" music video series that reinvents songs from the show's score.
"It's amazing. I love it!" he said.
"It's really exciting and fun. By the time a show gets on, I've written these songs and heard them over and over and over again... Then to hear someone take them and do something else with them — I love the thing that Mika and Ariana Grande did: their riff on 'Popular.' I just love it. It's so much fun to hear someone take one of those ideas and just take off with it."