Ecuador finished level with Mexico on four points after the teams drew 0-0 in Group B but Sanchez's side secured a place in the knockout stages thanks to their superior goal difference.
Venezuela advanced as group winners while Mexico and Jamaica were eliminated.
Sanchez told reporters that his side were under no illusions about the scale of the take they face in the last eight against Group A winners and World Cup champions Argentina at the NRG Stadium in Houston, Texas on Thursday.
"We know it is an unmatched opponent, and we know how tough it's going to be, but our players are happy that they've moved to the next round, and we'll see how that unfolds," he added.
"It is yet another final for us, and we will try to compete against the world's champion and the world's best team... I believe that our team is going to be extremely motivated with a very high morale and trying to play a good match.
"I have full confidence in our players. I know that they are going to give their best as they've done in the three matches. We know how tough it is, but it is 11 against 11, and we're going to do whatever we can to win it."
Ecuador failed to cause any real problems for Mexico in an underwhelming performance and Sanchez acknowledged the team had plenty to work on.
"We know that we still have a lot of work ahead of us to keep evolving, but this is Copa América, and we also need to understand the great progress we've made today because we are moving to the next round," he added.