Both Japan and Greece are fighting for their Group C survival following respective defeats to Ivory Coast and Colombia.

But after being outmuscled in a second half which saw Ivory Coast strike twice in the space of two minutes, the Blue Samurai face another bruising encounter in Natal's Estadio das Dunas on Thursday.

Thanks to the likes of Giorgos Samaras, Greece are likely to tower over Japan.

But Zaccheroni believes the determined approach which catapulted Greece to a surprise victory in the 2004 European Championships will prove a bigger threat to the four-time Asian champions.

"Greece have always stood out for their tenacity and the compact nature of their game," Zaccheroni told reporters on Wednesday.

"They've built their success on that. They withstand attacks very well, they're difficult opposition and so we have to exploit our opportunities when they come up.

"This is a very short tournament, so we all know that if you lose one match it gives you little chance of advancing.

"But I'm an optimist. Japan have significant potential. Now we're all just waiting to show that potential in our next two matches, starting with tomorrow.

"It's fundamental we win if we're going to advance."

Japan faced criticism for a tame second-half display against Ivory Coast which saw Wilfried Bony and Gervinho hit the net in the 64th and 66th minutes following the introduction of powerful forward Didier Drogba moments earlier.

A hugely disappointed Zaccheroni said he had expected "a lot more" from his players and that will be required against Greece and again when they play Colombia in Cuiaba on June 24.

But after four days of introspection, the 61-year-old former Juventus coach gave little away on the eve of their crucial match: "The team has understood what went wrong and now they know the mistakes they have to avoid tomorrow."

With Greece also fighting for their World Cup survival, a crunching encounter is on the cards. Accordingly, Japan captain Makoto Hasebe has spent four days trying to rally his troops.

"I spent some time talking to the players trying to gauge how everyone was feeling and to find out what they wanted to say. That's part of my role," said Hasebe.

"But I came away feeling that we are a far more united team."

Some of Hasebe's focus was spent raising the spirits of Shinji Kagawa, who was replaced in the dying minutes by Yoichiro Kakitani in the final minutes against Ivory Coast.

The Manchester United midfielder struggled to contain lively right-back Serge Aurier, who took advantage to help set up both of the goals in the Elephants' comeback win.

It crushed the morale of 25-year-old Kagawa who, admitting "pressure and nerves" had caused him to make mistakes, told Kyodo news: "I lost a battle with myself."

Zaccheroni is expected to make a number of changes to his starting line-up for a match that will decide whether Japan repeat their second-round feats of 2002 and 2010.

But Hasebe suggested the United midfielder will be given a second chance: "He is an important member of our team, so I think he will step up to the challenge."