Japan coach Zico accused his team of sitting back as they surrendered a lead in losing to Australia in their Group F opener in Kaiserslautern.
The Brazilian-born coach said: "We did not do anything after taking the lead, but we had two clear goalscoring chances on the counter-attack.
"But if you do not put the ball in at one end, you sometimes concede a goal at the other.
"The way Australia turned the game on its head is difficult to stomach."
Zico pointed to the heat in the Fritz Walter stadium as a factor in his side's lapses in concentration.
He said: "We wasted a great opportunity. We had our chances but it was so hot today it didn't help.
"It was 38 degrees but we lost concentration at a critical point and it cost us."