2021 MercedesCup – Singles

Singles
2021 MercedesCup
Champion	Marin Čilić
Runner-up	Félix Auger-Aliassime
Score	7–6(7–2), 6–3
Draw	28
Seeds	8

Marin Čilić defeated Félix Auger-Aliassime in the final, 7–6^(7–2), 6–3 to win the singles tennis title at the 2021 Stuttgart Open. It was Čilić's 19th career ATP Tour singles title, his first in three years, and he did not drop a set en route to the victory. The No. 47-ranked, 32-year-old Čilić also became the lowest-ranked winner since Juan Carlos Ferrero in 2011 and the third-oldest champion in tournament history. Defending finalist Auger-Aliassime was contesting for his first career singles title in his eighth final.^[1]

Matteo Berrettini was the reigning champion from when the event was last held in 2019,^[2] but he could not participate as he was still competing at the French Open upon the beginning of the tournament.

The top four seeds received a bye into the second round.

	Semifinals							Final
		Marin Čilić	6	1
	WC	Jurij Rodionov	3	0r
									Marin Čilić	77	6
								3	Félix Auger-Aliassime	62	3
	3	Félix Auger-Aliassime	6	7
		Sam Querrey	4	5

	First round							Second round							Quarterfinals							Semifinals
								1	D Shapovalov	6	62	6
		F López	6	6					F López	2	77	3
		A Popyrin	4	4											1	D Shapovalov	5	63
		M Čilić	7	6												M Čilić	7	77
	WC	R Molleker	5	3					M Čilić	6	6
	WC	D Brown	3	64				5	N Basilashvili	3	2
	5	N Basilashvili	6	77																			M Čilić	6	1
																						WC	J Rodionov	3	0r
								4	A de Minaur	68	6	6
		G Pella	3	4					J Thompson	710	3	4
		J Thompson	6	6											4	A de Minaur	6	3	64
		D Koepfer	6	3	2										WC	J Rodionov	3	6	77
	WC	J Rodionov	2	6	6			WC	J Rodionov	5
	Q	P Gojowczyk	5	6	6			Q	P Gojowczyk	3r
	LL	I Ivashka	7	4	2

	First round							Second round							Quarterfinals							Semifinals
	6	U Humbert	6	6
		M Fucsovics	3	1				6	U Humbert	711	6
		J Chardy	4	4				WC	Y Hanfmann	69	2
	WC	Y Hanfmann	6	6											6	U Humbert	65	68
		G Simon	4	5											3	F Auger-Aliassime	77	710
		L Harris	6	7					L Harris	3	64
								3	F Auger-Aliassime	6	77
																						3	F Auger-Aliassime	6	7
	7	A Mannarino	3	2																			S Querrey	4	5
	Q	J Duckworth	6	6				Q	J Duckworth	4	67
	Q	A Çelikbilek	4	1					S Querrey	6	79
		S Querrey	6	6												S Querrey	64	77	6
	Q	R Albot	64	65											WC	DS Stricker	77	64	3
	WC	DS Stricker	77	77				WC	DS Stricker	77	77
								2	H Hurkacz	65	65

	First round							Qualifying competition
	Alt	Luke Saville	78	4	4
	Alt	James Duckworth	66	6	6
								Alt	James Duckworth	77	3	7
								8	Ilya Ivashka	65	6	5
	WC	Daniel Masur	0	64
	8	Ilya Ivashka	6	77

	First round							Qualifying competition
	Alt	Sergiy Stakhovsky	1	64
	Alt	Peter Gojowczyk	6	77
								Alt	Peter Gojowczyk	6	6
								Alt	Grégoire Barrère	2	4
	Alt	Grégoire Barrère	6	6
	5	Marcos Giron	3	2

	First round							Qualifying competition
	3	Jiří Veselý	77	2	4
	Alt	Dennis Novak	65	6	6
								Alt	Dennis Novak	6	63	5
								Alt	Altuğ Çelikbilek	1	77	7
	Alt	Altuğ Çelikbilek	6	2	6
	6	Lucas Pouille	3	6	3

	First round							Qualifying competition
	4	Emil Ruusuvuori	7	6
	Alt	João Sousa	5	3
								4	Emil Ruusuvuori	65	4
								7	Radu Albot	77	6
	Alt	Christopher O'Connell	3	0r
	7	Radu Albot	6	0

• Main draw
• Qualifying draw