During his 24 seasons in Nippon Professional Baseball, he played for the Chunichi Dragons, the Orix BlueWave, and the Tohoku Rakuten Golden Eagles.

He helped lead the Dragons to the 1999 Japan Series (which they ultimately lost to the Fukuoka Daiei Hawks, 4-games-to-1).

On April 1, 2007, José Fernández and Yamasaki hit grand slams in the same inning for the Tohoku Rakuten Golden Eagles.

Yamasaki led the Pacific League in home runs and RBI in 2007, also being selected for a Best Nine Award as a designated hitter.

Yamasaki played 24 years in NPB, retiring after the 2013 season with 403 home runs, placing him 17th all-time in Japanese professional baseball.