The South Americans booked their spot in Sunday's final against Germany by winning a penalty shootout against the Dutch, following a goalless draw.
"We played a brilliant game, without any fear of anything," he told reporters. "We came into the game of our lives and now we will enjoy it because this is a once-in-a-lifetime opportunity.
"Hopefully we will be crowned champions on Sunday but, regardless of the outcome, I have no words to express how proud I am ... the goal was to be in the final."
Mascherano has made 104 appearances for his country.