Japan revived their hopes of reaching the Confederations Cup semi-finals, as Greece suffered a second group defeat.
Oguro came on as substitute for Japan
Japan should have scored more than one goal, with strikers Atsushi Yanagisawa and Keiji Tamada guilty of a series of terrible misses in a one-sided game.
With 14 minutes left Japan finally scored, Masashi Oguro tucking the ball past Antonis Nikopolidis.
Japan keeper Yoshikatsu Kawaguchi was only tested by an Angelos Haristeas shot in a poor display by Greece.