Novak Djokovic of Serbia is set to play Daniil Medvedev of Russia in the U.S. Open final on Sunday, with Djokovic looking to become the most successful male tennis player in history with 23 Grand Slam singles titles. This marks the end of the Big Three era in men's tennis, with Djokovic having already won two more major titles at the Australian Open and French Open this year. The last American man to win the U.S. Open singles title was Andy Roddick in 2003.