Tennis' future takes center stage on the second day of the U.S. Open.

The focus will be on youngsters seeking to wrest major titles from the game's Big Three, the return of defending champion Naomi Osaka and the first main-draw appearance at Flushing Meadows for 15-year-old American Coco Gauff.

Novak Djokovic, Rafael Nadal and Roger Federer have combined to take 11 Grand Slam titles in a row, so the speculation is who can succeed them. Dominic Thiem, Alexander Zverev, Stefanos Tsitsipas and Nick Kyrgios all will make their case Tuesday.

Nadal will be there too, with a night match against Australian John Millman, who stunned Federer last year in New York.

Gauff takes on Anastasia Potapova of Russia.