The Japanese face Paraguay in Pretoria on Tuesday in the second round and, while no Asian team has recorded a victory over a South American opponent at a World Cup, Japan have built up a head of steam and are flying.
Cautious Okada, however, warned against complacency in the Japan camp and said it was important to build on their success in South Africa rather than resting on their laurels.
"If you pile up bricks only vertically they will fall at some point," Okada told a news conference on Monday.
"I don't want to make a judgment based on only one result or one competition, we need to have a longer-term vision in order to evaluate the real level of Japanese football."
Japan sealed second spot in Group E with a convincing 3-1 win over Denmark, and Okada said progressing to the next stage would be a boost for Japan and good for Asian football in general.
"South Korea, unfortunately, lost to Uruguay (in the second round) but I think they played wonderfully," he added. "As the only remaining Asian team at this level we really would like to get to the last eight.
"For Japan's football community it would be bright, wonderful news. It would be one step closer to their goal of becoming one of the world's top teams if we get to the last eight."
NOT ATTRACTIVE
Paraguay had not captured the world's imagination in terms of stylish football but their quality could not be ignored, said Okada.
"Perhaps Paraguay are not one of the most attractive teams, but fundamentally they are strong," he added.
"In the group phase they finished first ahead of some very good teams. Many of their players are in European leagues and up front in particular they are very quick."
Japan's success in South Africa is in stark contrast to their pre-World Cup struggles. Okada had offered to resign just over a month ago after his side were beaten 2-0 by South Korea in a friendly in Saitama.
Frequently bashed by Japanese media in the run-up to the World Cup, Okada's stock rose dramatically after first round victories over Cameroon and Denmark but he was sceptical that it would stay that way.
"I don't read all that stuff. I'm not aware of what the press is saying about my reputation," he added. "It fluctuates and changes and it will do so again in the future. I don't care, I will just go my own way."
