Japan coach Alberto Zaccheroni has warned that the Blue Samurai are growing in confidence and getting better by the day after overcoming a shaky start to reach the Asian Cup quarterfinals.

They cut down fellow three-time champions Saudi Arabia 5-0 on Monday to finish on top of Group B with two straight wins following a cliff-hanging 1-1 draw with dark horses Jordan, which also made the knockout stage.

Super-sub Shinji Okazaki scored a hat-trick and fellow forward Ryoichi Maeda struck twice on Monday evening as Japan crushed the Saudis without suspended goalkeeper Eiji Kawashima and injured World Cup hero Keisuke Honda.

"We have lagged behind other teams in preparation. To catch up with them, I hope to help the team develop at this tournament," the former AC Milan boss said.

"We did better in the second match than in the opener and we did better in the third than in the second. I'm glad to see the team growing like that."

After the Jordan draw, Japan came back to life with a thrilling 2-1 win over Syria, in which Kawashima was sent off.

It has taken it time to gel in Doha with Zaccheroni unable to have a proper training camp ahead of the tournament with 10 of the team plying their trade in Europe.

Several players, including Okazaki, could join the squad only after New Year's Day when the prestigious Emperor's Cup tournament in Japan ended.

"The team is reacting well to what I tell them," the coach said.

"I'm very satisfied as they have delighted me with great football at times.

"The only issue I might as well mention is that they have room to grow in the area of personality," the 57-year-old Italian said without elaborating.

"As far as I can see, there are no easy games at this tournament. I feel it is a very great tournament which has convinced me that Asian football is in the process of growing."

In the last eight, Japan faces Bruno Metsu's Qatar, which forced it to a 1-1 draw in a 2007 Asian Cup group match, in what will be a tough test in front of that team's home fans.

Qatar sprang back from a 2-0 opening defeat by Uzbekistan to beat China and Kuwait under the tutelage of well-travelled Frenchman Metsu, who guided Senegal to the 2002 World Cup quarterfinals.

"They have rebuilt themselves after losing their opener and I believe they have the momentum going on further," said Zaccheroni.