The sexy songstress was experiencing butterflies in her stomach right before stepping onstage for her first-ever Saturday Night Live performance last weekend – until Timberlake cracked a joke.
"My heart was beating so fast," the R&B diva, 23, tells PEOPLE exclusively. "Everything is so fast-moving there. You just start freaking out."
Enter the hero. "Before I went on," says Ciara, "he made me laugh, which made things light and not so serious. It just felt like, 'We're gonna have a good time.' We had a lot of fun. We're silly together."
Timberlake – who was hosting SNL for the third time – and Ciara, the musical guest, performed the steamy "Love, Sex, Magic," from her new album, Fantasy Ride.
Her first foray on the long-running NBC show "was awesome," she says. "Being with Justin on SNL is one of the experiences that will go down in my book as one of the most fun experiences I've ever had. Absolutely. He cracks me up."
He even had her laughing when they heated up the set of the "Love, Sex, Magic" video, where they stand oh-so-close, lick each other and brush their lips up against each other – and perform some scandalous dance moves. "In the middle of it, you had to do what you had to do but afterwards it was funny," she says. "You go from one take where you are rubbing on somebody's neck and biting on his ear and then it's like, 'Cut! We gotta do it again!' and he's got his finger down your lip. It was funny."
Helping School KidsOn a more serious note, to help millions of kids gain access to supplies they need for school, Ciara has teamed with DoSomething.org and Staples for the 2nd annual National Do Something 101 School Supply Drive, to encourage teens to make a difference by collecting school supplies for kids in need and dropping them off at their nearest Staples store.
Staples customers can get involved by donating $1 at any Staples store from July to September, with 100 percent of the proceeds benefiting local kids in need.
To kick-off the campaign, Ciara is starring in a public service announcement to air on Channel One, BusRadio, MySpace, Facebook and TV and radio stations nationwide.
"The Do Something campaign is awesome because it encourages people to provide school supplies for kids," says Ciara, who shot the PSA Tuesday night in Los Angeles. "Some of the supplies are expensive and some people can't afford them. Nowadays in this economy, education has become more important than ever. We need to do whatever it takes to empower our kids to help them to move forward and be the best that they possibly can be. That's why I wanted to get involved."