Brazil hope their second-half collapse against Japan will be a wake-up call ahead of their World Cup campaign.
Carlo Ancelotti's men went into Tuesday's international friendly in Tokyo on the back of Friday's 5-0 triumph at South Korea but came back down to earth against Japan, who celebrated their first-ever win against the five-time world champions.
Brazil led 2-0 at half-time but Japan punished the visitors' defensive errors to win 3-2.
"A second-half blackout by the entire team," Brazil captain Casemiro told Sportv. "If you sleep for 45 minutes, it could cost you a World Cup, a Copa América, a medal, a four-year dream. The whole team wasn't at its best in the second half, and it's the details. At this high level, it's the details that make all the difference. We know there was an extra boost of enthusiasm [following the win against South Korea].
"We wanted to end this 12-day preparation on a high note. And perhaps we threw away our excellent preparation in 45 minutes. So, let this be a lesson learned, the World Cup is here. We need to play at a high level, no matter if it's against Japan or whoever as 45 minutes can cost you a childhood dream."
Paulo Henrique and Arsenal's Gabriel Martinelli had given Brazil a comfortable lead.
However, Fabricio Bruno's misplaced pass allowed Takumi Minamino to reduce the deficit early in the second half before Bruno sliced an attempted clearance into his own net to draw Japan level. Ayase Ueda then headed the winner.
"Individual mistakes don't affect a player's presence on the team," Ancelotti said regarding his team's defensive errors.
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"What we have to evaluate is the team's reaction after the first mistake, which wasn't good because we lost some of our balance on the field and our positive thinking. We have to learn from our mistakes in the second half. The team's biggest mistake was not reacting well after the first goal. It's a good lesson for the future. We have to learn from this defeat.
"I think until Fabrício's mistake [in the first goal] we controlled well the game. The team then lost its mentality after the first mistake. That was the team's biggest mistake.
"We'll continue doing tests during the FIFA window in November. This doesn't change our approach. I think we need to be balanced in what we do. The team played very well against South Korea, played well in the first half [against Japan], and very poorly in the second half. It's a process, and in the World Cup, we need balance."