Complex sentence: This system matched the team with the best first-half record against the team with the best record in the second half; the winner of this best-of-five series series advanced to the Japan Series, where they played against the CL champion.
Split into simpler sentences: This system matched the team with the best first-half record against the team with the best second-half record. The winner of this best-of-five series advanced to the Japan Series, where they played against the CL champion.