Though both songs were estimated to sell about the same number by the week's end, Katy Perry's "Roar" may now outsell Lady Gaga's "Applause" two to one in the first week at retailers, according to industry forecasters.

"Roar" was slated to be revealed on Monday (Aug. 12), but leaked early over the weekend; Gaga's "Applause" also had an early leak over the weekend, though her new single wasn't supposed to hit until Aug. 19. "Roar" kept its Monday release date, "Applause" moved up to Tuesday, Aug. 13.

The timing discrepancies and promotional periods may account for part of the reason now that experts are telling Billboard that Katy Perry may move about 450,000 digital copies of "Roar" by the end of the first week tracking period on Sunday and Lady Gaga may sell about half of that, between 200,000 and 225,000. The charting forecasters initially said the two pop singles may sell neck-and-neck sums at around 400,000 each based on early indicators.

In the period leading up to the holiday shopping season and year-end lists, big albums and singles have always been in competition at the marketplace. Sets from Lady Gaga and Perry (and Justin Timberlake, and Drake, and Jennifer Lopez...) are naturally getting a back-to-back comparison due to the circumstances from the weekend and their indisputable realm of the popular music marketplace. Lady Gaga and Katy Perry have Tweeted support at each other and tried to, in some ways, diminish the "competitive" aspect to the singles sales race, even both are putting the hard-press on their fans through social networks.

Katy Perry and Lady Gaga have each released lyric videos for their respective singles, which you can watch below. They will both perform at the 2013 MTV VMAs on Aug. 25; Perry's album "Prism" is due Oct. 22 and Gaga's "ARTPOP" will be out Nov. 11.

HitFix Poll

Which new pop single do you like better, Lady Gaga's or Katy Perry's?