The 30-year-old was keen to identify the defensive improvements as Germany returned to winning ways following a frustrating draw with Ghana on the weekend.
"We made big step forward," Lahm told reporters. "We did better than against Ghana. We can be absolutely satisfied.
"That's what makes our team strong - that we are very defensive, that everyone defends. That is what's important in a tournament like this.
"I had the feeling that the team really works together - in the defence as well in the attack, and that's a good feeling."
Finishing top of the group means that Germany will face Algeria in the last 16 on Monday.