After a bad season that saw his Hertha Berlin team relegated, Friedrich, who in the past played as right-back, did not believe he would make it to the June 11-July 11 tournament.
However, strong performances in warm-up games saw him reinforce his position at the heart of the defence.
"Everyone knows I have a tough season behind me. I thought my chances of playing here were only small," the 31-year-old told reporters.
"But I have matured and I feel more comfortable in the central defence. In that position you are more involved in organising the game and that suits me more," he said.
Friedrich, who is looking for a new club, said he would most likely play as the left-sided centre-back with Mertesacker on the right.
KLOSE TO START
Friedrich, who has won 72 caps, said Germany would probably start with the same team which began their final friendly 3-1 win against Bosnia and also included out-of-form striker Miroslav Klose.
"I am not the coach but I think that the way we played against Bosnia will also be the formation we will play here," he said.
Disappointing Klose netted only three times in the league in the past season and Germany scored all their goals against Bosnia when he was taken off for in-form striker Cacau.
But fellow defender Mertesacker also believed the 31-year-old Klose, top scorer at the 2006 World Cup, would start against Australia.
"We support each other and I think Miro is an experienced World Cup player and can best evaluate himself. So I trust him when he says he will be in form. The team is fully behind him," said Mertesacker.
Germany, who also play Serbia and Ghana in Group D, must not drop any points against the Australians, given they are eager to quickly book their spot in the second round, Mertesacker said.
"A lot can happen in three games and so we want to reach a satisfactory number of points very quickly," he said. "So it would be bad if we lose to Australia. That would not be a good start and it is something I do not even think about."
