Not once, but twice.
Of course, she was not clapping for herself.
First Jackie applauded the dance performance of William Levy and Cheryl Burke, who danced the Viennese waltz while Jackie sang "Ava Maria" for classical night.
Later in the show, Jackie sang "Dark Waltz" during the pro dance performance with Tristan MacManus and Karina Smirnoff.
"Vote for Katherine Jenkins on dancing with the stars!" Jackie tweeted.
"So looking forward to seeing my friend @jackieevancho at DWTS tomorrow... Here's a clip of us singing together: (see video above)," tweeted Katherine Jenkins.
"@KathJenkins can't wait to see you too!!! It's been so long since we've seen each other!!" Jackie tweeted back.
The two sang "Silent Night" at the Rockefeller Center tree lighting in 2010.
A year ago, Jenkins was the musical guest on DWTS's classical night. She said she never imagined she would be a dance contestant a year later.
The 8 p.m. show opened with violinist Joshua Bell playing "Vivaldi's Summer" accompanied by the DWTS pro troupe.
Jackie, the 12-year-old soprano prodigy from Richland Township, and Italian tenor Vittorio Grigolo sang, accompanying dance performances throughout the evening.
"Very excited to be singing on DWTS for classical week," Jackie tweeted on Wednesday. "Hope to see Katherine again. She's so wonderful."
After Jackie's first song, her father, Mike, tweeted a "review":
"@JackieEvancho made me very proud once again with her Ave Maria on Dancing With The Stars!"