The 22-year-old struggled towards the end of the Premier League season for Chelsea and that, combined with some under-par international form, saw his place in Luiz Felipe Scolari's starting XI questioned.
|5/2||Oscar is 5/2 with William Hill to score the first or last goal v Mexico|
"I didn't have to prove anything to anyone," he told FIFA.com. "If I did [need to prove something], then it was only to Felipao [Scolari], and he always showed total faith in me.
"Of course in friendly games you don't have quite the same edge. A World Cup is a different matter though, as I proved. And not just to Felipao, to the whole world."
Oscar's goal was notable for its nature - a 20-yard toe-poke that flew into the bottom-left corner, giving Croatia goalkeeper Stipe Pletikosa little chance.
And he said his poked shot was due to fatigue, but that it was something he had practiced before.
"It was a real toe-poke. At times like that, anything goes," he added. "Most of the lads in our team used to play futsal and we learned to strike it with our toes. [Because of cramp] it was the only option I had left."