Jannik Sinner, of Italy, holds up the championship trophy after defeating Taylor Fritz, of the United States, in the men's singles final of the U.S. Open tennis championships, Sept. 8, 2024, in New York. Credit: AP/Julia Nikhinson

The two young champions, who met as teen-agers, are expected to face off at this year’s U.S. Open. A new book by Giri Nathan tracks their parallel ascent.