Bayern head coach Pep Guardiola switched to four in defence later on in the game as the champions eventually secured a 2-1 victory, and Lahm believes that there is still plenty of work for the players to do before they hit top form.
"We started with a three-man backline," Lahm told the official Bundesliga website. "But then we realised it was putting us at a disadvantage out wide, and that we weren't able to close down the spaces well enough so we switched to four at the back.
"I think it took us the first quarter of an hour to get into the game, and then we played very well until the 60th minute, but towards the end you could see that we were running out of steam a bit."
Bayern continue their Bundesliga campaign against Schalke 04 next Saturday.