The concert was packed when Wiz, who grew up in Pittsburgh, appeared on stage and sang "Black and Yellow," as fans went wild. The optics were pretty spectacular ... flames shooting up in the air with yellow lights surrounding the venue.

Morgan and Wiz embraced as they left the stage. Seems Wiz is a Morgan fan ... he's hit up several of the country star's concerts.

If you checked our site earlier, you'll know the concert went down at PNC Park ... it's where some women got into a pretty epic porta-potty brawl the day before!