Who was the Opponent in the match with a Score of 6–3, 6–4?
CREATE TABLE "singles_14_6_8" (
  "outcome" text,
  "date" text,
  "tournament" text,
  "surface" text,
  "opponent" text,
  "score" text
);
SELECT "opponent" FROM "singles_14_6_8" WHERE "score"='6–3, 6–4';