Japan coach Alberto Zaccheroni said his team were not cohesive enough as they slumped to a 2-1 defeat to Ivory Coast on Saturday.
The Asian giants appeared to be on track for victory in their FIFA World Cup opener thanks to Keisuke Honda's 16th-minute strike at the Itaipava Arena Pernambuco.
Instead, Japan were left to pick up the pieces after Wilfried Bony and Gervinho both scored in the space of two minutes just past the hour-mark as Ivory Coast kicked off their Group C campaign on a winning note.
"The players gave 100 per cent but we were not cohesive enough," Zaccheroni told FIFA.com post-game.
"After we took the lead, we did go on the back foot, but that was because of our opponents' attacking qualities.
"Not through our own choosing where they really pushed us back. That especially happened on the wings."
Zaccheroni introduced Yoshito Okubo and Yoichiro Kakitani in search for an equaliser but it never came and the Italian had called for improvement ahead of fixtures against Greece (Thursday) and Colombia (June 24).
"Despite my substitutions, I was not able to change the course of the game," he said.
"We were not aggressive enough and we need to improve on that because we've been playing better than that.
"We can play better than that – and we will work on that in our next two games."