The Stuttgart striker scored twice in the first half before grabbing a late third while Ryoichi Maeda scored a brace to ensure Japan finished top of Group B.

Alberto Zaccheroni's side will tackle Qatar for a place in the semi-finals on Friday.

Japan needed at least a point to be assured of qualification for the last eight but they were clearly hungry for victory and they opened the scoring with just eight minutes on the clock through Okazaki.

Yasuhito Endo spotted the forward's run between the Saudi defence and Okazaki lobbed the keeper before making certain the ball landed in the back net by stabbing home from close range.

It got even better for the Japanese just five minutes later when Okazaki got his second of the game as he was left unmarked inside the area to head home from Shinji Kagawa's cross.

And the win was in no doubt when Japan added a third in the 19th minute when Maeda volleyed home from close range.

Despite their dreadful start, the Saudis finally began to enjoy a spell of possession after that - perhaps due to Japan opting to step down a gear - and they had chances through Osama Al Harbi, Tayseer Al Jassem and Abdullah Suhail.

But normality resumed six minutes into the second half when Maeda headed home his second from a Masahiko Inoha cross.

With no sign of a way back, the Saudi players clearly could not wait for the final whistle to be blown while Japan were seemingly happy to relax and take their foot off the pedal.

But there was time for Okazaki to score his third of the game when he latched onto a pass from Maeda in the 80th minute, worked his way past a couple of defenders before smashing home.