The U.S. Open is one of the most exciting traditions in the world of tennis. Serena Williams took down her sister Venus on Tuesday in a highly-anticipated quarterfinals match, and if she wins her final two matches, she'll be the fourth woman in tennis history to achieve the calendar grand slam. 

It's a high-stakes tournament, which is why the faces of the players -- as they relish in victory and wallow in defeat -- are so emotional. Here are some of the most iconic facial expressions of 2015 U.S. Open, in all its raw, vulnerable glory. 

The event runs from Aug. 31 to Sept. 13 at the USTA Billy Jean King National Tennis Center in New York City.