NEW YORK :Mexico's Renata Zarazua pulled off a stunning upset by beating sixth seed Madison Keys while American Frances Tiafoe launched his latest bid to end the American men's drought at the U.S. Open with a confident win over Japan's Yoshihito Nishioka. Keys finally claimed her maiden major at the Australian Open this year but produced 89 unforced errors in the first match of the day on Arthur Ashe Stadium as she became the highest seed in the tournament to fall in a 6-7(10) 7-6(3) 7-5 defeat.