Kim Lammers scored twice on Tuesday as defending Olympic women's hockey champion the Netherlands beat Japan 3-2 to move to the top of Group A.
The Netherlands beat Belgium 3-0 in its first match. For Japan, it was the second defeat of the tournament after losing its opener 4-0 to host Britain.
Lammers scored in each half to bring her tournament tally to four goals and Ellen Hoog smashed in a powerful shot for the Dutch.
Rika Komazawa, who had to leave the pitch in the first half after being hit in the face by a stick, scored with 24 minutes to go and Japan drew closer when Aki Mitsuhashi deflected a penalty into the Dutch net seven minutes later.