Question: For what round was the opponent Nikola Ćirić Dušan Vemić?
SQL: SELECT "Round" FROM "2-18042031-16" WHERE "Opponents" = 'Nikola Ćirić Dušan Vemić';

Question: What was the surface when the result was 6–7 (6–7) , 7–6 (9–7) , 6–7 (4–7) , 7–5, 3–6?
SQL: SELECT "Surface" FROM "2-18042031-16" WHERE "Result" = '6–7 (6–7) , 7–6 (9–7) , 6–7 (4–7) , 7–5, 3–6';