Carlos Alcaraz won the Cincinnati Open on Monday after Jannik Sinner was forced to retire due to illness. Alcaraz was already up big on Sinner, the World No. 1, when he had to retire. Sinner told the crowd that he hoped to play after feeling bad overnight, but he couldn't make it work.

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.