Speaking after the game, he said: "It is hard to compare Vietnam in this game with the first leg. They only had one shot [at goal] in this game and scored from [it]. In the first leg they had seven shots. But I am not surprised by Vietnam's display. I knew that they would play defensively."
The hosts dominated the game with 73 percent possession and 24 shots but could only score one goal.
It was the first time in 60 years Japan failed to beat Vietnam. In the first leg last year they had won 1-0 in Vietnam thanks to a Junya Ito goal.
This time Vietnam scored early, in the 20th minute, from a Nguyen Thanh Binh header.
After that they simply sat on the lead, defending in numbers, making it hard for Japan to find a way into the box. They did manage to find the equalizer in the 54th minute through a Mayo Yoshida tap-in, but could not score again, and the game ended 1-1.
Moriyasu said: "My players have forgotten to mark the opponent. We cannot let this happen again in the future. I am sorry that we could not win this game, sorry we could not get a seventh consecutive win."
Japan entered the game already having qualified for the 2022 World Cup.