It was always going to be a big chart battle - two of pop music's princesses going head-to-head with their eagerly-awaited new singles.
But it would seem that Katy Perry has won the first round after her single Roar sold twice as many as Lady Gaga's Applause in their first week of release.
According to Nielsen SoundScan, Roar shifted 557,000 copies in the US last week, making it her biggest weekly tally of her career so far.
Katy Perry's Roar is outselling Lady Gaga's Applause in the US (WENN)
It has also ended a nine-week non-consecutive run at the top of Billboard's Digital Songs chart by Robin Thicke's Blurred Lines featuring TI and Pharrell Williams.
Lady Gaga's Applause though, only sold 218,000 copies, just 39% of the opeing tally of Perry's single, and making it debut at number three.
Roar is from Perry's upcoming album Prism, which will come out in the UK on October 21, while Applause's parent album Artpop will be released on November 11.
But Gaga has come out on top in the UK where Perry's song has yet to be released (WENN)
But Gaga may fair better with her single in the UK - Roar has yet to be released commercially but Applause was rush-released last week after it was leaked online and debuted at number five on the Official UK Singles Chart.
She took to her Twitter page on Monday to bemoan the leak and wrote: "'Due to hackers an abundance of low/high quality leaks... We issue this pop music emergency... Monsters spread the word."
Roar was also leaked but it didn't stop Perry's official US release, although Gaga reached out to her on Twitter and wrote: "Wanna grab some shovels and f*** up some hackers?"