There was a moment at Wimbledon last July that felt like it might define a career in the most bittersweet way possible. Grigor Dimitrov, 34, had Jannik Sinner two sets down on Centre Court.

Going into their first meeting, Federer was No. 1 in the world and Nadal was a 17-year-old unknown upstart. Yet it was Federer who left not only with a straight-set loss, but with ...