Zimling made his debut for the club on 2 February 2013 against German giant Bayern Munich, coming on as a 62nd-minute substitute, in a 3–0 loss. Three weeks later on 23 February 2013, he scored his first Mainz 05 goal, in a 1–1 draw against Wolfsburg. Three days later on 26 February 2013, Zimling scored his second goal for the club, in a 3–2 loss against SC Freiburg. Since joining Mainz 05, he quickly established himself in the midfield position for the rest of the season. At the end of the 2012–13 season, Zimling went on to make fourteen appearances and scoring two times in all competitions.
