"We haven't got anything yet," Okada said after Monday's convincing home victory. "It won't be an easy game like this when we play away."
Japan, seeking a fourth straight berth in the World Cup finals, will play Oman again in sweaty Muscat on Saturday and then face winless Thailand in Bangkok before hosting Bahrain later this month. Monday's win was vital for Japan's hopes of qualifying for South Africa in 2010 and took the pressure off Okada after his side were beaten 1-0 by unfancied Bahrain in their last qualifier in March.
Celtic's star midfielder Shunsuke Nakamura, playing in his first World Cup qualifier under Okada, scored a goal and set up another against an Oman side who lacked five key players due to suspensions and injuries. "I don't think we've got over the mountain yet. But we made our first step forward," said Okada, describing the opponents as nothing of the "real Oman."
Bahrain, who beat Thailand 3-2 away on Monday, remain at the top of the Group Two table with a perfect nine points, followed by Japan, the former Asian champions, with six points. Oman have three points. The group's top two finishers will advance to the final Asian qualifying round.
"Three shots revive Japan," declared a headline in the influential daily Asahi Shimbun. But the business daily Nikkei cautioned: "A big win on one night is just a passing dream." It pointed out that Oman would be back to full strength on Saturday with the return of suspended players.
Okada, who took over from Ivica Osim last December after the Bosnian suffered a serious stroke, has been under scrutiny after the defeat to Bahrain, with some questioning his tactics. He had admitted that a draw or defeat on Monday might have cost him his job, according to the Sports Hochi daily.
The result delighted Japan Football Association president Saburo Kawabuchi. "The match was rich in substance," he told reporters. "I am looking forward to seeing how the team will play hereafter."
Okada, in his second stint as national coach after guiding Japan to a winless World Cup finals debut, called up European-based players including Nakamura for the first time. The others were two midfielders, new St Etienne signing Daisuke Matsui and VfL Wolfsburg's Makoto Hasebe.
"We were all right in scoring two goals when the pressure was a bit slack. Then we slowed down in moving the ball. Shunsuke's goal early in the second half made it easy for us," Okada said. "We could have scored more on crosses. But in any case, I thank the players for fighting to the last minute."
Nakamura, who turns 30 this month, said: "Every one of us went out aggressively. "When we play away, we'll get hurt if we feel like loosening up after 3-0. We must fight and keep working as hard as we did."