opening (in a game of go, chess, etc.)
early stages; initial phase; outset
序盤から手が読めない。
The opening is impossible to read.
映画の序盤は静かで眠くなった。
The opening of the film was so quiet it made me drowsy.
序盤こそ苦戦したが後半に逆転した。
We struggled in the early stages but came back in the second half.