Iggy Azalea

Iggy Azalea, shown here on stage at last week's opening celebration at SLS Las Vegas, gave a surprise performance at Horseshoe Casino Baltimore on Tuesday night. (Ethan Miller / Getty Images for SLS Las Vegas / August 23, 2014)

Nothing says "Surprise!" like an Australian rapper with three Top 10 songs currently on the Billboard Hot 100.

Last night, Iggy Azalea — the 24-year-old pop-rap artist responsible for the inescapable hit "Fancy" — performed a surprise five-song set at Horseshoe Casino Baltimore's three-level bar, 14Forty, to celebrate the casino's opening. 

She was not the only surprise. Gladys Knight took the stage for a 45-minute set as the doors opened at 9 p.m., and Pauly D, of "Jersey Shore" fame, DJ'd a 90-minute set as well. 

Noah Hirsch, vice president of marketing for the Horseshoe, said it took a "good group of team members" to keep the surprises a secret. Preparation began months ago, he said.

"The entertainment and focusing on 14Forty is something we kicked around at the end of last year and beginning of this year," Hirsch said on Wednesday. He said 14Forty will host local and regional music acts seven days per week, with bigger "surprises sprinkled in" once in a while.

Azalea, whose other Top 10 hits include "Black Widow" and a guest feature on Ariana Grande's "Problem," will return to the area on Sept. 25 for a headlining concert at Pier Six Pavilion.