Lahm was originally signed as a back-up for Andreas Hinkel, who played as right back, but coach Felix Magath moved him to the left back position, on which he toppled the German international Heiko Gerber. He made his Bundesliga debut on the first day of the season 2003–04 against Hansa Rostock as he came in as a substitute left back in the 76th minute for midfielder Silvio Meissner. He made his first professional start as a left back on the fourth matchday as a 63rd-minute substitute for Gerber and his first game over the full 90 minutes followed on the sixth matchday against Borussia Dortmund. Thereafter he established himself as a regular left back for Stuttgart. On 29 September 2003, Lahm made his first Champions League appearance as a starter against Manchester United. On 3 April 2004, he scored his first ever Bundesliga goal in a 5–1 away win for Stuttgart against VfL Wolfsburg. During the 2003–04 season Lahm appeared for Stuttgart in 31 Bundesliga and seven Champions League matches overall and came second in the election for the German footballer of the year.