2017: ATP debut Molleker made his ATP main draw debut at the
German Open in Hamburg after defeating, in the qualifying rounds,
Casper Ruud and
Leonardo Mayer, who later won the tournament as a lucky loser.
2018: First Challenger title & ATP and top-10 wins Molleker won his first
ATP Challenger Tour title as a wildcard at the
Heilbronner Neckarcup, defeating
Jiří Veselý in the final. He won his first match at ATP-level at the
Stuttgart Open, defeating compatriot
Jan-Lennard Struff in the first round. At the
2018 German Open in Hamburg, as a wildcard, he beat former world No. 3
David Ferrer in the first round.
2019: Grand Slam and top 150 debut Molleker made his Grand Slam debut at the
2019 Australian Open, battling through three qualifying rounds before falling to world No. 16
Diego Schwartzman in four sets. At the
2019 BMW Open he recorded his third ATP win over
Marius Copil as a wildcard. He also entered the doubles event with
Andre Begemann as an alternate pair. He defeated two-time Hamburg champion Leonardo Mayer to record his fourth ATP singles win.
2021–2025: Out of top 400 In 2021, he received a wildcard for the
2021 MercedesCup in Stuttgart, but lost to
Marin Čilić. He received a wildcard in doubles at the
2021 Hamburg European Open partnering
Daniel Altmaier. He received a wildcard for the main draw at the
2023 Hamburg European Open but lost to compatriot and wildcard
Maximilian Marterer. Ranked No. 179, he also received a wildcard for the main draw at the
2024 BMW Open, and defeated qualifier
Francesco Passaro for his fifth ATP win. ==Singles performance timeline==