When Novak Djokovic (36) slumped to the ground after three hours and 50 minutes of mind-boggling, awe-inspiring, barely believable tennis against Carlos Alcaraz (20) in Cincinnati, minds already began to wander to Flushing Meadows and a potential showpiece final at the US Open. The duo may be 16 years apart in age, and the Serb may be in his twilight years, but there is little doubt that they are both the present AND future of men's tennis.