Katy Perry 'to triumph over Lady Gaga at singles chart'!

Lady Gaga and Katy Perry are going head-to-head in a superstar single showdown at the Billboard singles chart.

Industry forecasters have predicted that Perry's new song 'Roar' will sell 450,000 downloads by the end of the week, Contactmusic reported.

They have also claimed that Gaga's, whose new track 'Applause' was released prematurely, is tracking to move around 225,000 downloads, probably enough to take second place.