The Bavarians' captain was unhappy with his side's display on Saturday despite coasting to victory, and felt the media furor in the lead-up to the game did not help matters.
The Bavarians maintained their nine-point advantage over second-place Bayer Leverkusen, but even with the notable positive, the defender was unimpressed with a sluggish showing.
"I think today we were far from perfect, over the full 90 minutes that was not a good game," Lahm told reporters. "It is difficult, you come from the first round, then the winter break and then comes the first game and it is sometimes hard to focus."
Lahm also touched on the news of Guardiola joining the club and the subsequent attention surrounding the appointment may have had something to do with the lackluster performance.
“The turmoil of recent days have played a part," Lahm said.
Meanwhile, Bayern midfielder Javi Martinez revealed his delight at the arrival of the former Barcelona boss and said the squad was brimming with excitement at the chance to work with the renowned coach.
“Working with one of the world’s best coaches is a huge motivation for me; I, as well as all of my teammates here welcome him with open arms," Martinez said. "Anyone who knows about football knows who Guardiola is and that he has done everything. We are really happy that he's coming."