CREATE TABLE table_name_27 (winning_score VARCHAR(255), margin_of_victory VARCHAR(255), runner_s__up VARCHAR(255))
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"