NEW YORK (AP) — No need for any extra practice after this performance by Serena Williams. Plus, it’s not as if she needs to study too hard to figure out how to deal with her next opponent. Playing the best she has in the U.S. Open as she chases a calendar-year Grand Slam, Williams set up a quarterfinal against older sister Venus by making only six unforced errors in a 6-3, 6-3 victory over 19th-seeded Madison Keys on Sunday.