Takamatsu was chosen as one of the Designated Players for Development by J. League and JFA in 1999 when he was a student of Tatara Gakuen High School. Because of this status, he was able to register as a Sanfrecce Hiroshima player while he was still eligible to play for his high school club. However, he did not play any official match for Hiroshima.
After graduating from his high school in 2000, he joined J. League Division 2 side Oita Trinita. He played 6 games and scored 1 goal in his first season. In the 2001 season, he became a regular playing 22 league games and scored 8 goals. The club was promoted to J.League Division 1 at the end of the 2002 season.
He was part of the Japanese 2004 Olympic football team, who exited in the first round, having finished fourth in group B, below group winners Paraguay, Italy and Ghana.