American Serena Williams was knocked out in the fourth round of the French Open by Kazakhstan’s Elena Rybakina on Sunday, losing 6-3 7-5 to the 21st seed. Williams, 39, was below her best as her wait for a record-equalling 24th Grand Slam singles title went on. Rybakina held her nerve superbly to reach her first Grand Slam quarter-final, sealing victory as Williams struck a backhand return out.