There were no reports of a tsunami threat, injuries, or major damage
Ryoichi Maeda also struck twice, either side of half-time, as the Blue Samurai avenged their loss to the Saudis in the 2007 semi-finals, which denied them a record third straight continental title.
Japan had needed just a point to qualify after a draw with Jordan and a 2-1 defeat of Syria.
The Green Falcons had already crashed out of contention with two losses to Syria and Jordan.
It is only the second time in Asian Cup history that Saudi Arabia have not made it to the knockout stages.
The Blue Samurai shrugged off the absence of suspended first-choice goalkeeper Eiji Kawashima and two injured key midfielders, Keisuke Honda and Daisuke Matsui.
Ace striker Yasser Al Qahtani attemped the first Saudi shot in the second minute when he trapped a through pass and floated the ball wide.
Shimizu S-Pulse striker Okazaki, filling in for CSKA Moscow’s Honda, missed a chance two minutes later when he narrowly failed to meet Maeda’s cross towards Saudi goalkeeper Waleed Adbullah.
But Okazaki, reportedly nearing a deal with Stuttgart, opened the scoring on eight minutes, trapping a long ball from Yasuhito Endo in the box, lifting the ball over Abdullah and slotting it into an open net.
The 24-year-old, who scored the final goal in Japan’s 3-1 win over Denmark at the World Cup group stage, doubled the score in the 13th minute as he banged home a cross from Borussian Dortmund rookie Shinji Kagawa with a breath-taking diving header.
Maeda, the top J-League scorer, made it 3-0 for Japan six minutes later, hooking home a volley from a Yuto Nagatomo cross.
The Saudis fought hard to pull one back on the half hour, with Taisser Al Jassam shooting straight at Japan’s second-choice custodian Shusaku Nishikawa. Abdullah Shuhail then fired a left-footer far over the bar.
Kagawa received an Endo cross and beat Abdullah one-on-one in the box before losing control of the ball.
After the break, Japan continued their onslaught with Maeda scoring again on 51 minutes when he headed home a right-wing cross from Masahiko Inoha.
Japan kept possession and the Saudis could not convert any of their limited chances, with Mohammed Al Shalhoub’s dangerous corner on the hour safely caught by Nishikawa.
Okazaki’s third goal came in the 80th minute when he took a short pass just on the edge of the box and slammed a left-foot shot past Abdullah.
Al Shalhoub attempted a free-kick three minutes later from 25 metres but Nishikawa responded sharply to punch it away.
There were no reports of a tsunami threat, injuries, or major damage
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