Jannik Sinner, of Italy, reacts after defeating Alexei Popyrin, of Australia, during the second round of the U.S. Open tennis championships in New York.

Jannik Sinner, of Italy, shakes hands with Alexei Popyrin, of Australia, after winning their second round match of the U.S. Open tennis championships in New York.

Fans wait for autographs from Jannik Sinner, of Italy, during the second round of the U.S. Open tennis championships in New York.

Jannik Sinner, of Italy, returns a shot to Alexei Popyrin, of Australia, during the second round of the U.S. Open tennis championships in New York.

Jannik Sinner, of Italy, returns a shot to Alexei Popyrin, of Australia, during the second round of the U.S. Open tennis championships in New York.

Jannik Sinner, of Italy, returns a shot to Alexei Popyrin, of Australia, during the second round of the U.S. Open tennis championships in New York.

Alexei Popyrin, of Australia, returns a shot to Jannik Sinner, of Italy, during the second round of the U.S. Open tennis championships in New York.

Alexei Popyrin, of Australia, returns a shot to Jannik Sinner, of Italy, during the second round of the U.S. Open tennis championships in New York.