Victoria Azarenka, of Belarus, returns a shot to Viktoria Kuzmova, of Slovakia, during the first round of the U.S. Open tennis tournament, Monday, Aug. 27, 2018, in New York. [Photo: AP/Adam Hunger]

Serena Williams returns a shot to Magda Linette, of Poland, during the first round of the U.S. Open tennis tournament, Monday, Aug. 27, 2018, in New York. [Photo: AP/Julio Cortez]

Denis Shapovalov, of Canada, serves to Felix Auger-Aliassime, also of Canada, during their first-round match at the U.S. Open tennis tournament, Monday, Aug. 27, 2018, in New York. [Photo: AP/Julio Cortez]