Katy Perry Covers Rihanna, Willow Smith + Jay-Z

Pop princess Katy Perry gave fans in Lisbon, Portugal a taste of American Top 40 with a string of cover songs from Rihanna, Willow Smith and Jay-Z.

Perry slowed down her show with an intimate acoustic set, which included a mash-up of cover songs including Rihanna's 'Only Girl (In the World),' Jay-Z's 'Big Pimpin',' and Willow Smith's catchy hit, 'Whip My Hair.'

The 'Firework' singer had the whole crowd singing along to Rihanna's big hit, and though the Barbadian singer wasn't in attendance, Perry wished her a happy birthday on stage -- she turned 23 on Sunday.

Perry kicked off her 'California Dreams' tour on Feb. 20 in Portugal.

Watch Katy Perry's Cover Song Mash-up