The Poland international netted a fine goal in the dying seconds of the match to seal the win for the reigning champions - having previously already equalised after a corner from Douglas Costa - controlling Franck Ribery's cross on his chest before finding the bottom corner with a volley.
"My first thought was to pass the ball straight away, but that was not easy because there was nobody there yet," Lewandowski told reporters.
"I then just wanted to control the ball, play it simple and try anything. Fortunately, I succeeded. I did well to control the ball and then had a bit of luck. I did not hit the ball as clean as I wanted to, but a goal is a goal.
"We fought right until the end and eventually succeeded. That is the Bundesliga for you. Our opponent defended well. We had to be patient. It was important to win the first game after the restart.
"It is never easy against Freiburg, who are very organised and tactically strong. They did well both in defence and in attack."
Head coach Carlo Ancelotti, meanwhile, was pleased to see Bayern emerge victorious after a complicated match.
"It was a difficult game, because we faced a strong and aggressive opponent," the Bayern boss told reporters.
"We did not put in a good performance in the opening 45 minutes. But I liked the desire and the character that the team showed. That is why we won the game in the end.
"We cannot be happy with the way we played, but we can be happy with the result."