The two giants will meet in a major finals for the first time in over a decade, and Otamendi is aware of the significance of the meeting
The best performance Lionel Scaloni's side have managed in the tournament to date secured a meeting with the hosts in Belo Horizonte next Tuesday and Otamendi reflected on their improvements from a shambling start to the group stage.
"We knew it would be difficult from the beginning. It took time to take off, we got better," the Manchester City centre-back told reporters.
"Now we are in the semi-finals against an opponent where it is a clasico and we hope it will go in favour of Argentina."
Otamendi came out on top in an absorbing duel with Venezuela striker Salomon Rondon as a previously porous Argentina backline showed signs of finding their feet.
"We knew it was going to be a difficult, hard and very intense match," he said.
"The important thing was to keep discipline, with very strong players like Rondon who hold [the ball up] well.
"We controlled the game very well for most of the time. Maybe from dead balls the opponents had a few chances.
"The goal in the second half gave us a cushion. We were attacking and we knew how to keep organised well. It's a great victory for us."
Otamendi's club team-mate Sergio Aguero, whose shots led to both Argentina goals, was similarly fired up by the prospect of taking on Brazil.
"We will try to do our best, as we have been doing, to work for the shirt," he said.
"Argentina-Brazil is not played every day, especially in a competition like this. It generates a lot of expectation, not only in our country but in the world.
"We knew that this match was not going to be easy but we are happy to have gone to the semi-finals. Little by little we are getting better."