Fans were briefly evacuated from Lincoln Financial Field during singer Raye's opening set.
Some expressed shock and disappointment, while others sang and waited it out in the rain.
Stadium officials told people to shelter in place until the severe weather moved out.
The show, which was scheduled to start at 7 p.m., resumed around 10 p.m. for those drenched but dedicated concertgoers.
Bruno Mars performs again at the Linc Wednesday night.
Action News Meteorologist Karen Rogers says Wednesday's Bruno Mars concert in South Philadelphia looks better than it did on Tuesday after a weather delay.