The midfielder believes that triumphing over the Selecao would stand them in good stead going into the World Cup
La Roja reached Sunday's showpiece by beating Italy on penalties in the semifinals while the Selecao needed a late winner from Paulinho to send them through the last four at Uruguay's expense.
The Barcelona playmaker believes that victory would both confirm Spain's international dominance of late and give it a vital psychological boost over the coming 12 months against the tournament's hosts.
"It could be a very important step for them and for us too," Fabregas told AS. "We know that the only thing left for us to do is beat Brazil and if we achieve that we will give ourselves a new challenge to see if we can win the World Cup again.
"We would then be plotting the conquest of our second World Cup with more confidence, knowing that we can beat the World Cup hosts. It would be a big mental step in our favor and against them.
However, Fabregas is wary of the dangers that come with playing against a side with significant home support and hinted his perception that Spain's status as the world's top side turns the crowd in favor of its opponent.
"In every stadium we’ve played in, the crowd have wanted us to lose," the ex-Arsenal skipper noted.
The 26-year-old also had words of praise for new Barca teammate Neymar, who has been widely considered to be one of the players of the tournament, while also hailing Liga full backs Dani Alves and Marcelo for their ability to attack.
"Neymar’s a great player, he’s unpredictable, decisive, he’s great at dribbling, has a great pass and reads the game well," he continued. "I like him.
"Alves and Marcelo are two secret weapons, because if the team can’t create then they are the ones that drive their teams forward and attack. They are both brilliant full backs."