Katy Perry's new song Roar is expected to sell well with industry forecasters suggesting it will move around 450,000 downloads by the end of this week, outselling Gaga's Applause.
Applause is also showing promise of a good start with an expected number of 200,000 to 225,000 downloads, according to Billboard. Roar and Applause were released to digital retailers on August 12 and 13 respectively.
Perry's Roar is from her album Prism which releases on October 22 whereas Applause is the first single from Gaga's ArtPop, arriving on November 11.
Gaga has been spotted promoting the single by sporting face paint. Gaga's last studio album was 2011's Born This Way, which debuted at No 1 on the Digital Songs chart with 448,000 downloads after only three days on sale, according to Nielsen SoundScan. Perry's last new album, 2010's Teenage Dream, was ushered in by the single California Gurls. It bowed at No 1 on the Digital Songs chart with 294,000 downloads.