Scolari was in charge of hosts Portugal when they lost the opening game of Euro 2004 to Greece and his side went on to lose again to the same opponents in the final three weeks later.
"It is absolutely terrible to play the first match at home and lose it, it really is," the Brazilian said at the Mane Garrincha National Stadium.
"When Portugal lost the opening game to Greece in Porto in 2004 it was awful. You have nine points you are playing for in the first phase and losing that makes everything difficult, you create a bad situation for yourself.
"We have to win this opening match," added Scolari. "I do not agree with people who say Japan are not a skilful team with no history.
"They are the first team to qualify for the 2014 World Cup so they will be very difficult opponents. If we lose...we will have to do what we did in Portugal and win the next two games to qualify."
Scolari said he did not feel under any particular pressure apart from the typical demands made on Brazil when they play at home.
He brushed aside widespread criticism of his team following an average set of results since he returned as Brazil coach in November, 10 years after leading them to the World Cup crown in Japan in 2002.
"I am less anxious than I used to be when I was younger because I have learnt to control it and I sleep at the end of the day very easily," said Scolari.
"Of course there is pressure on Brazil but that is because we are always regarded as one of the big teams and are expected to challenge for the title.
"Playing in our own country is no different. Yes we have had some problems leading up to the tournament but in the two or three weeks we have been together we have largely overcome them."
Mexico and Italy are the other teams in Group A and play their first match on Sunday at the Maracana.
The Confederations Cup is a warm-up tournament for next year's World Cup in Brazil.
- Sports & Recreation