Brazil's women have never won gold and that wait will now extend until at least its home Olympics in Rio after goals from Yuki Ogimi and Shinobu Ohno helped Japan set up a semi-final meeting with France.
Brazil dominated possession throughout but could not make it pay as Marta, Cristiane and Renata Costa all missed chances to find the net.
And its wastefulness was punished by a clinical Japan as the world champion profited from its incisive counter-attacking, despite spending most of the contest penned back in its own half.
Barcellos has accused Norio Sasaki's team of putting up a defensive "wall" in an attempt to hinder Brazil's chances.
When asked if Japan was now favourite to win the tournament, he said: "If they play like they did today, they are not.
"If they play the way they are, defending and playing like a wall, then I don't believe they will.
"I am used to Japan playing from the back and passing the ball, this team that played today is not the team that has been playing, so they are not always going to be able to play like that and score.
"That was the difference today, they had two chances and they took them."
"We created a lot of opportunities and from what we created we deserved a better result."
Japan coach Sasaki, who had controversially instructed his side not to push for a winner late in its group game with South Africa to ensure it would stay in Cardiff for this game, agreed his side's approach had been defensive, but was unrepentant.
"Of course Brazil are a very great team and today I felt that as well," he said.
"The game was better than we expected, if we judge Brazil and Japan people might say Brazil are a better team.
"But in the Olympics we don't know what will happen and today we showed a good attitude to win, and I think we are a team that can go all the way to Wembley."
Sasaki also felt that drawing with South Africa to avoid a trip to Glasgow in the last eight had paid dividends.
He said: "If we hadn't had that result things might have been different and I would like to thank the players for doing a great job and putting on a spectacle."