An 86th-minute John Brooks header clinched a dramatic win for the United States in their opening Group G game against Ghana.
Clint Dempsey had put the USA ahead after just 29 seconds but the Stars and Stripes were made to pay for failing to increase their lead as Andre Ayew netted an equaliser with just eight minutes of normal time left on the clock.
Just when it looked as though the clash would end with the points shared though, Brooks headed home a corner to spark jubilant celebrations and give Jürgen Klinsmann's side a precious win.
Former Blue DaMarcus Beasley completed 90 minutes for the USA.
Joachim Löw's side sailed into a 2-0 lead after 32 minutes, thanks to a Muller penalty and a header from Mats Hummels. Then four minutes later and already with a mountain to climb, Portugal's task became even more difficult when Pepe was sent-off for an apparent headbutt.
Muller added a third before half-time and the victory was sealed as the Bayern Munich striker completed his treble on 78 minutes, condemning Portugal to their heaviest World Cup defeat.
The result sees Germany sail to the top of their group, with the USA now level on points.
Iran and Nigeria played out a 0-0 draw.
In a game of few chances, the Super Eagles dominated possession but were unable to find the target. Ogenyi Onazi and Ahmed Musa spurned their side's best opportunities, as the former's effort sailed wide before the latter almost netted a free-kick.
Iran's Reza Ghoochannejad fashioned his side's closest attempt but goalkeeper Vincent Enyeama was equal to it.
The draw leaves both sides sitting relatively comfortably in their group, after Argentina defeated Bosnia-Herzegovina 2-1 earlier this week.