Kuroda won over 10 games for three consecutive years from 2001. In 2003, he became the opening-day starter, taking over for former ace Shinji Sasaoka. He pitched poorly at the beginning of the season, but improved after the all-star break to end the season with 13 wins. He marked two wins as a reliever in the 2004 Summer Olympics, contributing to the Japanese team's bronze medal. In 2005, he led the Central League with 15 wins, and won the Best Nine Award and the Golden Glove. He continued his success in 2006, ending the season with a league-leading 1.85 ERA to solidify his reputation as one of the best pitchers in Japan. The last Japanese starter to end the season with an ERA below 2.00 was Masaki Saito in 1989. He also made his first save that year on October 16 against the Chunichi Dragons, and led the league in complete games over a six-year period from 1999 to 2005.