Table schema:
CREATE TABLE table_name_27 (winning_score VARCHAR, margin_of_victory VARCHAR, runner_s__up VARCHAR)

Question: What is the winning score where the runner-up is Robert-Jan Derksen and the margin of victory is 1 stroke?
SQL: SELECT winning_score FROM table_name_27 WHERE margin_of_victory = "1 stroke" AND runner_s__up = "robert-jan derksen"