Serena holds off young rival, reaches U.S. Open quarters NEW YORK (Reuters) - Defending champion Serena Williams overpowered fellow-American Sloane Stephens in an Arthur Ashe Stadium slugfest 6-4 6-1 to reach the quarter-finals of the U.S. Open on Sunday. Top-seeded Williams avenged a defeat to Stephens in the quarter-finals of this year's Australian Open with a brilliant display of power tennis against a rival who has made a case that she could be Williams' successor as the face of U.S. women's tennis. Williams, at age 31 trying to become the oldest women's U.S. Open champion since tennis turned professional in 1968, broke the 20-year-old Stephens in the 10th game to end a riveting 52-minute first set when a big forehand from the 15th seed sailed just wide. The 16-times grand slam winner then raced through the second set to set up a quarter-finals clash against 18th seed Carla Suarez Navarro of Spain, a 4-6 6-3 7-6 (3) upset winner against eighth-seeded Angelique Kerber of Germany. How excited are we about the future of American tennis? Williams asked, drawing roars from the packed crowd watching the fourth-round contest.