Beginning in the next cycle, 1963–1966, the round-robin tournament was replaced by a series of elimination matches. Initially the quarter-finals and semi-finals were best of 10 games, and the final was best of 12. Fischer, however, refused to take part in the 1966 cycle, and dropped out of the 1969 cycle after a controversy at 1967 Interzonal in Sousse. Both these Candidates cycles were won by Boris Spassky, who lost the title match to Petrosian in 1966, but won and became world champion in 1969.