Now 23, the former No. 1 junior talks life on the ATP Challenger Tour, tennis landscape in his nation and appreciating the likes of Italians Musetti and Arnaldi.

As I face the impossible task of putting my feelings about his retirement into words, my mind fills with nostalgic images—memories of moments lived and shared by Rafael’s side,” he writes.

Thanks to the Almaty Open's generous opportunity, the German became the first player born in 2007 to win an ATP match.

The Brit left TCU in May. Since then, he's won four Challenger Titles, faced the undisputed G.O.A.T. at Wimbledon, and has started a promising tour career at warp speed.

The American recorded 100th tour-level win of his career in Antwerp on Tuesday, defeating Botic van de Zandschulp—conqueror of Carlos Alcaraz at the US Open—in the first round of the indoor stop, 6-4, ...