名古屋巨蛋
Iwakuma began the 2004 season 12–0 and establishing a franchise record for most consecutive wins to start the season. He received the most fan votes among Pacific League starting pitchers for the NPB All-Star Game that year, starting Game 1 at Nagoya Dome on July 10, and pitched in the 2004 Athens Olympics as a member of the Japanese national team in August. He finished with a 15–2 record for the year, leading the league in both wins and winning percentage (.882) for the first time in his career. He also pitched in Game 5 of the MLB All-Star Series held in November, holding the MLB All-Stars to one run over seven innings to earn the win.