Pandora stock fell as much as 21 percent to $15.25 in after-hours trading Thursday following a poorly received third quarter earnings report.

The ad-supported Internet radio company delivered several bitter pills to investors and admitted it got dinged by customers sampling Apple’s launch of rival Beats One, along with the launch of its subscription streaming service, which was on a free trial during the quarter.

The number of hours of music streamed by Pandora grew by just 3 percent in the quarter — down from 25 percent a year ago. The number of active listeners grew by just 2 percent, to 79.4 million, down from 5 percent gain a year earlier.

The company reported revenue of $311.6 million, below Street expectations for $314 million. It also recorded a loss of 40 cents per share versus profit forecasts of 10 cents.

Pandora also confirmed an Oct. 14 exclusive report in The Post that it will pay $90 million to settle royalty payment on pre-1972 music releases, which are not covered by copyright law.

Chief Executive Officer Brian McAndrews said that he doesn’t expect any long-lasting damage from Apple’s rival radio service.

Pandora shares, up 7.6 percent on the year, fell 7 cents, to $19.19, on Thursday.