CREATE TABLE table_name_23 (opponent_in_the_final VARCHAR, surface VARCHAR, score VARCHAR)

In the surface of clay who was the opponent in the game resulting in a score of 6 4, 6 4?
SELECT opponent_in_the_final FROM table_name_23 WHERE surface = "clay" AND score = "6–4, 6–4"
SELECT "opponent_in_the_final" FROM "table_name_23" WHERE "6–4, 6–4" = "score" AND "clay" = "surface"