Japan had won all nine of their preliminaries for the 2026 finals without conceding a goal until Shogo Taniguchi sliced the ball into his own net at Saitama Stadium to give Australia the lead.
Moriyasu's side salvaged a point from a game they dominated when Australia's Cameron Burgess steered Keito Nakamura's low cross past his own goalkeeper with 14 minutes left to ensure Japan remain on track for an eighth straight World Cup appearance.
"I feel frustrated," said Moriyasu, who led Japan to the knockout rounds of the 2022 World Cup. "We wanted to earn the three points and make our fans happy.
"So far we had come to this point without giving away a goal and tonight we gave away a goal, an own goal.
"We could have fallen apart after that point but our players held on and kept calm to level up their play in order to catch up with Australia. They accepted the reality and carried on.
"The result is a disappointing one but I can evaluate the process our players followed during the game."
Japan lead Group C on 10 points after four games, with Australia, Saudi Arabia and Bahrain all on five as the teams battle for the group's two automatic berths at the finals in North America.
Next up for the Samurai Blue is a trip to Jakarta on November 15 to face Indonesia, who had drawn their opening three matches before losing 2-1 to China on Tuesday.
"We learned that it is difficult to keep winning in the final qualifying," said Moriyasu.
"Having played Australia today, we realised again that it is not easy at all to win in these final qualifiers.
"We will make sure prepare well and take it a match at a time."
