NEW YORK — No reason for any extra practice after this performance by Serena Williams.
Playing the best she has during this 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.
Serena took only 68 minutes to dismiss Keys, a 20-year-old American with formidable serves and forehands who simply was outplayed.
Already a winner of the past four major tournaments, including last year’s U.S. Open, Serena is trying to become the first tennis player to win all four in the same season since Steffi Gr…