Japan are the continent's top-ranked side but finished second in Group D behind Iraq after losing to the West Asian side while Moriyasu's side also failed to keep a clean sheet after conceding goals against Vietnam and Indonesia.
"It's a sign of respect when people say we're struggling at the Asian Cup because they have such high expectations," Moriyasu told reporters ahead of Wednesday's last-16 clash against Bahrain.
"We know we can play better but Asian teams are getting better and they are more competitive. The gap between top teams and lower teams have been cut, that's my impression."
Bahrain were the surprise Group E toppers after South Korea finished second and avoided a heavyweight clash between the two east Asian teams, but Moriyasu is wary of the threat of the Gulf nation who reached the knockout stage for just the third time.
"Bahrain are a very talented side, they have individual talents and they work collectively as a unit. They can not only counter-attack but they have talented players up front that can play good football," Moriyasu said.
"We have to learn from our mistakes in the first three games but that doesn't mean we have any worries in the defensive line. I'm confident my players will play up to 100% of their potential."
Moriyasu also does not want the match to go to penalties, especially after they were knocked out in a shootout at the 2022 World Cup where three players missed their spot kicks.
"We lost on penalties to Croatia at the World Cup so we always have to improve that, but what's important is we don't go to penalties. We need to finish the game in 90 minutes," he said, adding that he had not yet decided who would take penalties.
Bahrain coach Juan Antonio Pizzi said they will look to control the game and possession against Japan while the former Spain international also has a chance at redemption after losing to Moriyasu's side in the same round in 2019 when he was in charge of Saudi Arabia.
"The pressure (on Japan) is important and it could play into our hands," Pizzi said.
"Regarding avenging the loss in 2019, this is football and it gives us the opportunity to patch our wounds. Some wounds heal on their own... However, life goes on and we must always be ready to accept what life throws at us.
"The psychological aspect is important for players especially when we win matches and qualify, the morale is high. Victory is good motivation, hopefully, we will be able to use that morale to come out victorious tomorrow."
