Table schema:
CREATE TABLE table_name_5 (opponents_in_the_final VARCHAR, score VARCHAR, championship VARCHAR, year VARCHAR)

Question: which opponents in the u.s. championships played after 1945 and had a score of 3–6, 6–4, 2–6, 6–3, 20–18?
SQL: SELECT opponents_in_the_final FROM table_name_5 WHERE championship = "u.s. championships" AND year > 1945 AND score = "3–6, 6–4, 2–6, 6–3, 20–18"