2021 MercedesCup – Singles
Matteo Berrettini was the defending champion from when the event was last held in 2019, but could not participate since he was still competing in the 2021 French Open at the beginning of the tournament. Marin Čilić won the title, defeating Félix Auger-Aliassime in the final, 7–6, 6–3. This was 8th consecutive final loss on ATP Tour for Auger-Aliassime. Seeds. The top four seeds received a bye into the second round.