Alexander Zverev of Germany returns the ball to Daniil Medvedev of Russia during their singles final tennis match of the ATP World Tour Finals, at the Pala Alpitour in Turin, Italy, Sunday, Nov. 21, 2021. (AP Photo/Luca Bruno)

Daniil Medvedev of Russia returns the ball to Alexander Zverev of Germany during their singles final tennis match of the ATP World Tour Finals, at the Pala Alpitour in Turin, Italy, Sunday, Nov. 21, 2021. (AP Photo/Luca Bruno)