The 'Tik Tok' singer was spotted kissing the Scottish dance music artist - who she supported on his 2009 UK tour - while sitting in The Front row of the show at the Rod Laver Arena in Melbourne on Tuesday night (08.03.11).
The pair were so into each other that they even left together before the end of the performance.
A source told the Melbourne Herald Sun newspaper: "They were getting right into it. They were practically fornicating."
Kesha was already in Australia and when she discovered Calvin was in the country as the support act for Rihanna she decided to fly to Melbourne so she could meet up with the 'I'm Not Alone' hitmaker.
Another source told The Sun newspaper: "They were all over each other and didn't care who was watching. Kesha is a bit of an animal but Calvin reckons he can handle her."
Calvin, 27, took to twitter on the night they hung out, revealing to his fans he'd had a "fun night".
He tweeted: "2nd Melbourne show with Rihanna went great! Lots of people in town for Future festival too so was a fun night! (sic)"
Kesha, 24, has previously revealed she learnt about sex at a young age, and admits her mother took an unusual approach to sex education.
She said: "I knew everything about sex before I was even seven. My mom left me at home when I was 14 with a credit card, and a box of condoms and the keys to the car and said, 'Don't get pregnant and don't drink and drive.' I had to be responsible for myself."