Ihara was rarely out of the spotlight in the emerging J. League throughout the 1990s. He spent most of his career with Yokohama Marinos and formed a key defensive partnership with the flamboyant Tsuyoshi Kitazawa at club level. After graduating from Tsukuba University, Ihara joined Nissan Motors SC (now known as Yokohama F. Marinos) and rapidly rose through the Marinos youth ranks to become a key player. The long-serving Ihara was so important to his club that he was nicknamed Mister Marinos by many Japanese fans. He formed the backbone of the club and also helped to bring on talented youngsters like Yoshikatsu Kawaguchi and Shunsuke Nakamura.