One of these days men's tennis is going to get boring again. There will be a fallow period. Greats will retire, get hurt, fatten up, open bad restaurants, babble on TV and buy vineyards. There will be a new, unremarkable No. 1. A murky two through 10. Maybe a U.S. player—a real-live U.S. player!—will crack the top five. Grand Slam finals will shrink to three uneventful sets. Tennis will return to that stale-aired foyer it got trapped in a while ago—dull, characterless, skippable.

That time isn't now. Men's professional tennis...