Shinji Okazaki scored a hat-trick while Ryoichi Maeda weighed in with a brace to ensure Japan finish top of Group B and set up a clash with hosts Qatar on Friday.

Japan had made a slow start to the tournament with a late Maya Yoshida strike rescuing a 1-1 draw against Jordan, but they have since gone from strength to strength with a hard-fought 2-1 win over Syria followed by their rout of the Saudis.

"I am very satisfied with this result," said Zaccheroni. "We have overcome the first obstacle of the Asian Cup, which was to get through the group stage and we are improving game by game at this tournament.

"In any competition we like to get the good results. I was a little worried about making mistakes but we did not. The players had a great performance.

"Japan is a very young team. I have selected young players. I am very satisfied with how they have performed and sometimes they play great football."

Japan will need to maintain their form against a Qatar side that has also been improving as the Asian Cup has progressed, an observation that was also noted by Zaccheroni.

"They have come back from their first match defeat and have the momentum," said the Italian. "At the same time Japan is in good condition as well so I expect the next game will be a great match."

The defeat for Saudi Arabia brings to an end a sorry campaign that has seen the 2007 finalists fail to pick up a single point.

But coach Nasser Al Johar vowed that the Green Falcons will bounce back, saying: "The Saudi national team is very strong, sometimes we suffer setbacks but always we recover.

"I regret what has happened but hopefully the Saudi officials will help us overcome this and do what needs to be done for the future."