SALVADOR, Brazil — Thomas Mueller had a hat trick as Germany routed 10-man Portugal 4-0 in their World Cup Group G opener Monday.

Mueller, who led the 2010 World Cup with five goals, was ruthless against a weak Portugal team that was clearly outplayed despite the presence of Cristiano Ronaldo.

The German team celebrated its 100th World Cup match with a rousing victory that was virtually assured by halftime.

Germany always aims to have an impressive start, and it certainly did this time. Four years ago, it started with a 4-0 win over Australia and reached the semifinals.

What must be worrying for Germany’s opponents is the apparent ease with which Joachim Loew’s lineup disposed of the fourth-ranked team in the world. Germany faces Ghana on Saturday and the United States on June 26.

Mueller scored on either side of Mats Hummels’ headed goal as Germany took a 3-0 lead at halftime and added his third goal in the 81st.

Portugal was already 2-0 down when Pepe was red-carded in the 37th minute for head-butting Mueller when the German player was sitting on the ground.

Nigeria 0, Iran 0: In Curitiba, Brazil, Nigeria and Iran delivered the first draw of the World Cup as they ground out a scoreless stalemate in Group F.

After a first half in which Nigeria failed to capitalize on its dominance, chances were few and far between in the second.