Coco Gauff, 18, reaches US Open quarterfinals for 1st time

Nick Kyrgios, of Australia, moves to return a shot to Daniil Medvedev, of Russia, during the fourth round of the U.S. Open tennis championships, Sunday, in New York. (AP Photo/Adam Hunger)

Coco Gauff, of the United States, serves against Shuai Zhang, of China, during the fourth round of the U.S. Open tennis championships, Sunday, in New York. (AP Photo/Eduardo Munoz Alvarez)

NEW YORK — Coco Gauff raised a fist, then wagged her right index finger, responding to, and riling up even more, a loud-louder-loudest Arthur Ashe Stadium crowd that was standing and screaming. Gauff’s U.S. Open opponent, Zhang Shuai, covered both ears with her hands to shield them from what she described later as a “Boom!” of sound.