Whether or not Serena Williams wins her "calendar Slam" next week, she has already made history. For what is believed to be the first time, ticket prices for the women's final of the U.S. Open are more expensive than the men's final.

Serena Williams of the United States returns a shot to Kiki Bertens of the Netherlands during their Women's Singles Second Round match on Day Three of the 2015 US Open.

And, for the first time, the women's final has sold out before the men's.