Yamaguchi was born in Sakawa, Kochi on April 17, 1978. He joined JEF United Ichihara (later "JEF United Chiba") from their youth team in 1996. He debuted on March 20, when he was 17 year and 354 days old. It was the youngest player to play for J1 League until Yuki Abe made new record in 1998. He became a regular player as center back from 1997. He moved to Gamba Osaka in 2001. The club won the champions 2005 J1 League, 2007 J.League Cup, 2008 and 2009 Emperor's Cup. He was also selected Best Eleven for 3 years in a row (2006-2008). In Asia, in 2008, the club won the champions AFC Champions League and the 3rd place Club World Cup. In 2012, he rejoined his first club, JEF United Chiba and played for the club in 3 seasons. In 2015, he moved to Kyoto Sanga FC and retired end of the 2015 season.