The actress' impromptu performance went down during a commercial break. She and the late-night host, 42, gushed over the '90s R&B group before she sang a few lines from the 1990 hit. Fallon was so impressed with her skills (those high notes!) that he gave her a standing ovation.
"They were, like, my girls. I was obsessed with them," Hudson, 37, said.
The Deepwater Horizon star has showed off her talent before. She previously rocked out to Elton John's "Tiny Dancer" when she played Penny Lane in the beloved 2000 film Almost Famous. Additionally, she sang on Glee when she had a recurring arc as dance instructor Cassandra July from 2012 to 2013.
Back in 2012, Hudson opened up about working on the Fox comedy. "[I had] nerves, but [I was] more excited, I think, because it’s like being a little kid again," she told Access Hollywood at the time. "Doing all three — singing and dancing and acting, and I love it. I just love it!"
Hudson is open to doing more music in the future. "I've always been scared of making music because I like authentic [songs]. I like music that feels really honest. I love pop music! But I write music and it's super depressing," she told Fallon on Tuesday night.
"I want to do it. I think I'm just going to do it for the sake of doing it and see how it turns out. Why not?" she added. "That's kind of how I feel. I'm old enough now where it doesn't really matter anymore. Music is my life and it's my first love."
Watch Hudson on The Tonight Show in the video above!
Can't get enough of Us? Sign up now for the Us Weekly newsletter packed with the latest celeb news, hot pics and more!