Jessica Pegula, of the United States, greets Ann Li, of the United States, left, after defeating her in the fourth round of the U.S. Open tennis championships in New York.

Jessica Pegula, of the United States, acknowleges the crowd after defeating Ann Li, of the United States, during the fourth round of the U.S. Open tennis championships in New York.

Jessica Pegula, of the United States, reacts after defeating Ann Li, of the United States, during the fourth round of the U.S. Open tennis championships, in New York.

Ann Li, of the United States, returns a shot against Jessica Pegula, of the United States, during the fourth round of the U.S. Open tennis championships in New York.

Jessica Pegula, of the United States, reacts during her match against Ann Li, of the United States, during the fourth round of the U.S. Open tennis championships in New York.

Ann Li, of the United States, reacts during her match against Jessica Pegula, of the United States, during the fourth round of the U.S. Open tennis championships in New York.

Jessica Pegula, of the United States, returns a shot against Ann Li, of the United States, during the fourth round of the U.S. Open tennis championships in New York.

Ann Li, of the United States, reacts after winning a point against Jessica Pegula, of the United States, during the fourth round of the U.S. Open tennis championships in New York.