Ariana Grande Hosts a Stage Crasher But Handles It Like a Pro

Ariana Grande never loses her cool in the middle of a performance ... even when creepy dudes crash her stage and get rushed by security.

Ariana was putting on a show Wednesday at the Wells Fargo Center in Philly, where some bro somehow got onstage and slowly crept his way toward her through the fog.

Security swoops in quick and yanks him away, yet stopped short of getting cops involved.

But watch how Ariana plays off the scary situation in the moment ... true pro.