Thomas Muller's hat trick thrust Germany into centre stage as Joachim Low's side demolished Portugal 4-0 in Salvador.
Portugal were already 2-0 down before they imploded completely with Pepe shown a straight red card for a light head-butt on Muller.
Germany, utterly dominant despite playing without a recognised centre forward, went on to win 4-0 with three goals for Muller -- the Golden Boot winner at the last World Cup -- and a thunderous header from Mats Hummels.
It meant a hugely disappointing result for world player of the year Cristiano Ronaldo, who had declared himself fully fit from his knee injury.
In Group G's other match, a late header from substitute John Brooks saw the United States claim all three points as they defeated Ghana 2-1 in Natal.
Clint Dempsey gave the U.S. the perfect start, winding his way through the Ghana defence before firing in off the far post with only 31 seconds played -- the fastest goal in the nation's World Cup history -- as they looked to avenge their round of 16 defeat to the Black Stars in 2010.
Ghana looked to have salvaged something from the game on 82 minutes, when Asamoah Gyan's clever backheel allowed Andre Ayew the space to find the net, but the U.S. swiftly restored their advantage Graham Zusi sent over a corner for fellow substitute Brooks to head home and secure the win.
Nigeria's attacking threat fell flat as they were held to the first goalless draw of the 2014 World Cup in their Group F clash with Iran in Curitiba.
Stephen Keshi's men produced a performance riddled with errors and few clear-cut chances. The Iranians, starting their fourth World Cup as one of the least fancied of all the finalists, arguably had the best chance when Reza Ghoochannejhad brought a fine save out of Nigeria keeper Vincent Enyeama in the 33rd minute.
Until that point the Africans had dominated possession but were hampered by a poor final ball, which kept their clear-cut chances to a minimum.