CREATE TABLE table_6647 ("Res." TEXT, "Record" TEXT, "Opponent" TEXT, "Method" TEXT, "Round" TEXT)

Opponent of sergei bondarovich, and a Record of 2 0 had what method?
SELECT "Method" FROM table_6647 WHERE "Opponent" = 'sergei bondarovich' AND "Record" = '2–0'
SELECT "Method" FROM "table_6647" WHERE "Opponent" = 'sergei bondarovich' AND "Record" = '2–0'