Japan captain Maya Yoshida urged his team to stick together after their 1-0 loss to Costa Rica on November 27 and believes a place in the knock-out round is still within their reach.
Yoshida said the Blue Samurai struggled to come down from the high of beating Germany in their opening game and found it "difficult" to prepare for Costa Rica, who were coming off a 7-0 thrashing by Spain.
Japan will likely now need at least a point in their final group game against Spain to progress and Yoshida urged his team-mates to pull off another famous win.
"We didn't have the same mentality as against Germany today, probably – that was our big mistake," Yoshida said, after losing to a Costa Rica side that scored in the 81st minute with their first shot on target.
"It's too easy to say we give up. Our strength is solidarity and unity. Again, we need to stick together and try to get the three points in the next game."
Japan looked a shadow of the vibrant side that roared back to stun Germany as they toiled against a defence-minded Costa Rica.
A win would have seen the Blue Samurai take a giant step towards the last 16 and Yoshida admitted they found the situation difficult to deal with.
"After the huge win against Germany and a big defeat for Costa Rica against Spain, it was a very difficult preparation, mentally," he said.
"I've been asking myself all the time for these past three days, are you ready? I asked that to the squad as well."
Japan had the lion's share of possession but failed to carve out many clear-cut chances against a Costa Rica side playing with five defenders.
Instead it was "Los Ticos" who scored with their only chance of the game, after a loose clearance by Yoshida allowed Keysher Fuller to fire off a shot that beat goalkeeper Shuichi Gonda.
"You have to take your chances and we didn't," said Japan defender Yuto Nagatomo.
"They hardly had any chances but when they had one, they scored from it. That's football.
"We have to accept this result but we're not finished yet. We have to get ready for the Spain game."
Japan manager Hajime Moriyasu made five changes from the starting line-up that beat Germany but said he had "no regrets" about how his team played.
He refused to push the panic button with one game still remaining.
"Spain are a strong team but we thought from the start that we would need three games to qualify so we'll keep preparing as normal," said the manager.
"Beating Germany doesn't mean we can beat Spain – both teams have won the World Cup and we have a lot of respect for them – but we did beat Germany.
"Spain will be a tough game but I think we have a good chance of winning."