Low's side beat the Portuguese 4-0 with Muller netting a hat-trick alongside Mats Hummels's first-half header, and the German boss praised his number 13 after the game.
He told reporters: "Thomas played very well up front. He kept Pepe and Bruno Alves busy the whole time. With his running paths he ripped the defence apart for other players – and he scored three goals. That's Thomas Muller.
"He is a very unconventional player. Even as a coach you don't know which way he will go sometimes."
Germany play Ghana on Saturday.