The Bayern Munich attacker scored the only goal of Thursday's game in Recife, his fourth of the World Cup so far, as DFB progressed to the last-16 alongside the Stars and Stripes.
Muller conceded that Germany had not found it easy against Jurgen Klinsmann's side but felt that they were the better team and also should be pleased with their improvement as the World Cup goes on.
"We were the clearly superior team from open play, especially at the beginning," the 24-year-old told ZDF.
"We did very well and then it was not so easy - the Americans dropped back very deep. It was a successful game. Although we only won 1-0 I am happy with it.
"We have done better than against Ghana in our overall play. We have big plans."
Muller's assessment of the game was slightly contradicted by his team-mate Mats Hummels, who stressed that the calibre of opposition should mean that no one should expect Germany to have an easy time.
"We gave a concentrated, but not a superior performance," the Borussia Dortmund defender added.
"We know that the U.S. are really good - the quality of the teams at the World Cup is too high to talk about easy games."