A Thomas Mueller hat-trick has inspired Germany to a 4-0 win over a dismal Portugal in their Group G clash in Salvador.

In a game billed as one of the biggest of the group stage, the Germans seized control when Mueller converted a penalty in the 11th minute and never let up.

Defender Mats Hummels nodded home from a corner not long after, before Portuguese defender Pepe was sent off for a ludicrously irresponsible head-butt on Mueller.

Against ten men, Germany was seldom troubled, and Mueller made it 3-0 just before half-time, capitalising on a loose ball in the area to prod home.

Portugal’s day got worse when defender Fabio Coentrao left the field with what looked to be a serious groin injury, before Mueller sealed the deal with his third from close range in the 78th minute.

Elsewhere, the USA enjoyed a 2-1 win over Ghana.

US captain Clint Dempsey scored the fifth-fastest goal in World Cup history after just 32 seconds to give the Americans a dream start.

Ghana equalised in the 82nd minute through a spectacular Andre Ayew strike.

But just when Ghana looked to have forced a draw, American defender John Brooks rose high to meet a corner and head home the winner on 86 minutes.

Brooks’ winner was sweet vindication for Jurgen Klinsmann’s selection policy. The tall defender was one of five German-born players controversially drafted into the squad by Klinsmann for the finals.

The 21-year-old Berlin-born player – the son of a US serviceman – represented Germany’s Under-20 side before deciding to pledge his allegiance to the United States in 2013.

“We have a great spirit and fight until the last minute,” said Klinsmann.

“It was a grind but it was a wonderful one at the end of the day. There is stuff we need to improve. We had problems with keeping the ball.”

Meanwhile, Iran and Nigeria played out the 2014 World Cup’s first draw, cancelling each other out in a scrappy 0-0 draw in Curitaba.

The match started at a lightning tempo, with Nigeria claiming the early ascendency but failing to find any quality with the final ball.

Iran negotiated its way back into the game, and had the match’s best chance when striker Reza Ghoochannejhad had a fine header brilliantly saved by keeper Vincent Enyeama.

Nigeria seemed the most likely to find a winner, but lacked polish in the final third, condemning the match as the first disappointment of the tournament.