Eminem was headlining the music festival when he brought out 26-year-old Rihanna as his special guest, reported Ace Showbiz.
The duo performed their two collaborations - 'Love the Way You Lie' and 'The Monster'.
Rihanna also took over the vocals for Eminem's 1999 hit 'Stan', which originally featured Dido.
The show marks Eminem's first headline set at Lollapalooza since 2011.
Both artists are set to go on the road together for their 'The Monster Tour: Eminem X Rihanna', which will kick off on August 7 in Pasadena, California.
'The Monster' was recently nominated for Best Male Video, Best Collaboration and Best Direction at this year's MTV Video Music Awards.