Ireland dominated possession and territory in the first half but couldn’t turn their advantage into goals.
Niamh Carey came within inches of setting up Emily Kealy for a tap-in, while Jessica McMaster saw her shot saved and Charlotte Beggs hit the outside of the post.
The Irish high-press was causing Japan to turn the ball over but a couple of other scrambles in the circle just didn’t fall their way.
Japan had only a few minutes of sustained pressure when they won four penalty corners in quick succession but they came to nothing.
There was more frustration for Ireland in the third quarter as Kealy saw another effort go wide and then from a deflection off the Japanese goalkeeper, somehow the ball came off Michelle Carey and over the crossbar.
With two minutes remaining, Ireland thought they’d scored. From a scramble in front of the goal, Katie Mullen poked the ball into the net from close range,
Irish celebrations were short lived when from an umpire’s referral, it was adjudged the ball hit the back stick of Mia Jennings.
Penalties were required and it was Ireland who held their nerve to advance in dramatic fashion.