The star was singing her 2008 hit Hot N Cold during a gig in the Australian city on Monday when a man crashed the stage and put his arm around her.
As seen in a video shared by fans on X, Perry quickly moved out of his reach as he kept jumping and dancing.
Two security guards then rushed the stage, while the man tried to avoid them.
"Well, there's never going to be another show like this. So just enjoy it, Sydney," Perry quipped.
She kept performing, while security were able to pull the man to the side stage, where two more members of security helped forcibly removed him.
While this incident was real, it follows a promotional skit in May when Perry halted a gig to tell a fan to stop messaging her fiancé Orlando Bloom.
During the US leg of her Lifetimes world tour, the Roar hitmaker paused her gig in Paradise, Nevada to single out an audience member named Kyle.
While addressing Kyle over private messages allegedly sent to her partner, Katy crouched on stage and told him: "I know why you're here. Listen, if you keep DM-ing my man ... you've been doing it for months, ever since the residency. You didn't come to see me play."
As the audience reacted with laughter and cheers, she continued: "If you keep on DM-ing my man I'm going to have you removed - seriously, get your own life."
The confrontation was later revealed to be a scripted segment of the performance, leading into her 2024 single I'm His, He's Mine.
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