Joachim Low’s side outclassed the Seleccao in their Group G encounter in Salvador last week with Portugal reduced to 10-men after Pepe was sent off for his first half headbutt on hat-trick hero Thomas Muller.
The big win was reminiscent of the World Cup four years ago when Germany demolished Australia in their first game before being stunned after losing 1-0 to Serbia in their second match in the competition.
And Neuer has warned his team-mates that they need to remain fully focused if they want to avoid a shock result against Ghana when the two sides meet in Fortaleza on Saturday.
"I think that we can only be partially satisfied with how we played," Neuer told the German Football Association's website.
"In assessing this game, we have to be honest: we got a penalty, they got a red card – basically everything went our way in this game.
"In the second half we controlled things with a man advantage but we have to realise that the opponent had opportunities. It wasn't all perfect."
Germany defender Per Mertesacker is set to feature in the match against Ghana – his 100th game for his country.
The Arsenal centre-back knows all too well how tough the African side can be after playing in Germany’s narrow victory against Ghana in 2010.
"It (the game) was on a knife edge the entire time," he said.
"But then we were saved thanks to Mesut Ozil's goal."