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.
His outstanding showing against Croatia silenced the doubters, however, and ahead of Tuesday's clash against Mexico, Oscar said public opinion mattered little to him.
"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.
"That's right, 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."