Horn blew away Chenoweth and the unsuspecting audience at the Hollywood Bowl with her considerable vocal abilities after backup singers randomly pulled her up on stage to sing "For Good," a duet from the Broadway musical Wicked, in which Chenoweth played the original Glinda.
A video of the performance quickly went viral after being uploaded to YouTube by Horn's friend, Mike Kestler. Horn commented on the page that the duet was not planned.
"I thought there'd be a plant too!" she wrote. "Apparently, Kristin gets a rush out of taking a musical gamble every once in a while. Haha!"
After her successful performance, Horn left the stage to find that she had impressed yet another celebrity, Darren Criss of Glee.
"When I went backstage, the first face I saw was that of Darren Criss who started immediately chanting my name." She wrote in a blog post for Broadwayworld.com.
As the stunned Horn headed home, she realized her outfit resembled something of the character Elphaba, whose part she had just sung.
"I didn't notice until after I'd left the Bowl that I was wearing a green shirt and a floor length green skirt with straight hair and black rimmed glasses," she wrote. "How much more Elphaba-looking can a regular gal get?"