In front of an expectant home crowd, Brazil were annihilated 7-1 by the Germans, with Muller scoring the first to take his tournament tally to five and overall World Cup total to 10.
"They were under a lot of pressure in their own country and in front of so many fans," Muller said after the match.
"It got to the point where I felt sorry for them because they've got so many fantastic players who didn't deserve to lose like that. Things like this only happen in football."
Germany will have to beat either Netherlands or Argentina in Rio de Janeiro on Sunday to win their fourth World Cup.