The U.S. Open enters its fourth round on Sunday, with American hopes Taylor Fritz and Taylor Townsend facing tough tests as Novak Djokovic battles through injuries to continue his quest for a record 25th slam. TOP MEN'S MATCH: TOMAS MACHAC V TAYLOR FRITZ Last year's finalist Taylor Fritz remains the home nation's best hope of becoming the first American man since 2003 to win the U.S. Open title following the exits of sixth seed Ben Shelton and 17th seed Frances Tiafoe in the third round. "Yeah,