Japan’s 38th minute goal from Kaisuke Honda has the up 1-0 at halftime over Cameroon.
A Daisuke Matsui cross found an unmarked Honda at the far post, giving the CSKA Moscow attacker an each finish to put the Japanese ahead.
It is the first time Japan has carried a lead into half of a World Cup match, with the Blue Samurai threatening to record their first World Cup win on foreign soil.
In a relatively evenly played first half, each team has managed one shot on goal while splitting possession. Both teams have had success attacking down their right sides, with Stephane Mbia putting in a strong half for Paul Le Guen.