Mana Iwabuchi scored in the 87th minute as Japan survived a scare on Saturday, defeating Australia 1-0 at Commonwealth Stadium.
Fourth-ranked Japan, the winner of the last World Cup in Germany in 2011 and silver medallists at the 2012 London Olympics, will remain in Edmonton to face the winner of Canada and England in the semifinals on Wednesday.
"We were confident we would score, even if we couldn't get one in the first 90 minutes," said coach Norio Sasaki. "I think the result of this match has given confidence to the Japanese players. I think what we did today can serve as a basis for future successes."
Japan had the best early opportunities, as Sinobu Ohno took a ball in full flight in the eighth minute and sent a chip shot just over the net. She also had a second glorious opportunity in the 22nd minute, narrowly missing the top corner.
Australia had a good chance in the 28th minute after Azusa Iwashimizu was yellow-carded for a body check, but Alanna Kennedy shot her free kick wide of the mark.
Japan responded in the 33rd minute with another great opportunity on a bullet of a shot from Aya Miyami, but Australian goalie Lydia Williams was able to make a leaping save to keep the game scoreless at the half.
Australia put on some more pressure in the 54th minute as a defensive miscue led to a shot from in tight by Samantha Kerr, but goalie Ayumi Kaihori was able to make the save.
Japan came close as well in the 60th minute as a back-foot redirection from Miyami went just wide.
The deadlock was finally broken in the 87th minute as Iwashimizu got a shot off in tight that was saved by Williams, but she corralled the rebound and chipped it over to sub Iwabuchi for the goal.
"She has a very good ability to create opportunities in front of the goal," said Sasaki. "She is a killer player. With her coming out against the tired Australian players, I told her that she was going to decide it."
The Japanese women are the only team to have won every game they've played in the tournament, previously defeating the Netherlands 2-1 in the Round of 16.
Tenth-ranked Australia advanced into the semifinal with a 1-0 upset of Brazil in their previous playoff match after playing in one of the tougher groups to start the tournament, losing 3-1 to the United States, before defeating Nigeria 2-0 and drawing 1-1 with Sweden.
"I thought the better team won today," said Australia head coach Alen Stajcic. "I thought Japan had a lot more patience and technique than us, especially in the first 20 minutes. I thought the game levelled out a bit after that, though... It's a heart-breaking experience for all of us, but sometimes you learn the most from these experiences.
"We're disappointed, but in the grand scheme of things, we lost 1-0 in the 87th minute to the defending champs, not 10-0. It's not as if we were humiliated."
Australia also played and lost to Japan in the final of last year's Asian Cup championships.