Katy Perry's 'Roar': an iTunes Best-Seller at 544,000 Downloads

The first song from "Prism" marks the singer's biggest career debut.

Katy Perry's new single, "Roar," was already projected to do big numbers in its first week out, but it looks like the tally is higher than anticipated. 

According to iTunes, the song -- the first released from her forthcoming album, Prism --  sold 544,000 digital tracks domestically since its Aug. 10 release, her best showing ever on the digital retailer.

Perry also announced today that she'll be closing out the iTunes festival in London on Sept. 30. Also on the monthlong bill are Lady Gaga, Elton John, Justin Timberlake, Jessie J, the Pixies and Arctic Monkeys.  

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As THR previously reported, "Roar" claims the biggest digital song debut of 2013, surpassing One Direction's "Best Song Ever," which tallied 322,000 for the week ending July 28. It also marks a career best for Perry, whose 2010 single "Firework" moved 509,000 unit sales for the week ending Dec. 26, 2010. Perry's biggest digital song debut to date was 2012's "Part of Me," which moved 411,000 in its first week out.

Twitter: @THRMusic