Goretzka's brace inside the first eight minutes set Joachim Low's side on the way to a comprehensive 4-1 victory over Mexico in Sochi.
Low's experimental squad have found Fisht Stadium to their liking, winning all three of their games on the Black Sea coast during the tournament and plundering 10 goals in the process.
But it was forced to come from behind to claim a 1-1 draw with Copa America holder Chile when the sides met during the group stage in Kazan and Schalke midfielder Goretzka believes his side deserved more for its efforts on that occasion.
"Personally I'm really happy to play against Chile again," he said.
"Why? Because in the earlier match against Chile we had a bit of a feeling that the draw was not enough for us.
"And now we can prove again that we can play against a really top-flight team. That's why we're here at the tournament to contest against these top teams."
The stellar showing from the 22-year-old will do little to dissuade speculation heavily linking him with a switch to Bayern Munich, after both his goals came courtesy of beautifully timed runs from deep and impeccable first-time finishes.
Asked whether Goretzka would be better used as a deep-lying or attacking midfielder, Low told reporters Germany has a complete player on their hands.
"I think he can do both. He can [play at] eight or six," said the long-serving head coach, who marvelled at Goretzka's lung-bursting runs.
"His special quality is he can run longer distances. Especially on the second goal, he is running from the midfield and crossing over the pitch with a great assist from Timo Werner.
"Running that long distance is what sets him apart from the rest and this is very hard to defend on the part of the opponent.
"He can play in different positions in the midfield because he's a really classy player."