After beating Portugal 4-0 in their first Group G encounter, Joachim Low's men drew 2-2 with Ghana, having to equalise through Miroslav Klose after the Africans came from behind to lead.
The Arsenal star admits that his team were not expecting such an intense game but argues that making some early mistakes will allow them to learn as the tournament goes on.
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"We are not playing like we should be but we haven't had that much time. We could not fully prepare for a match that intense.
"The match against Ghana was good for us in the sense of 'how can I hang on until the end?'" he added.
"We suffered and we experienced how it is to have to fight until the end and create chances. The match showed that we are ready to do that.
"It was a fine test and a fine challenge for the rest of our way and we're in a fine position; we just cannot afford to lose against United States [on Thursday].
"We found our way back into the match. That shows the high morale in our team. You could also see that the players who were brought on can make the difference."