NEW YORK—Nick Kyrgios sat in the Arthur Ashe Stadum locker room after ending Daniil Medvedev’s U.S. Open title defense and stay at No. 1 in the rankings and felt a mix of pride and relief. Pride at the big-serving, solid-returning performance that resulted in a 7–6 (11), 3–6, 6–3, 6–2 victory over Medvedev on Sunday…