Back in Rotterdam, Eenhoorn became player-manager of the Hoofdklasse team of Neptunus, during the seasons 1999–2001. All three seasons, Neptunus was most successful on a national level, since it both won in the Hoofdklasse (Dutch Major League) and the Holland Series. He was named Hoofdklasse Most Valuable Player as well as Coach of the Year in 2000, the first person to take both honors in the same year. The team also had international success when it won the World Port Tournament in 1999 and the European Cup in 2000 and 2001. In the 1999 World Port Tournament, Eenhoorn was named co-MVP with Ken Brauckmiller. Eenhoorn also played for the Netherlands national baseball team at the 2000 Sydney Olympics. He was not productive in those Olympics, going 3 for 26 with one walk, no runs and no RBI. He was caught stealing in both of his attempts.