Singles
2021 St. Petersburg Open
Champion	Marin Čilić
Runner-up	Taylor Fritz
Score	7–6(7–3), 4–6, 6–4
Draw	28 (4 Q / 3 WC )
Seeds	8

Andrey Rublev was the defending champion,^[1] but lost in the quarterfinals to Botic van de Zandschulp.

Marin Čilić won the title, defeating Taylor Fritz in the final, 7–6^(7–3), 4–6, 6–4.

Seeds

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

Draw

Finals

	Semifinals							Final
	Q	Botic van de Zandschulp	3	3
		Marin Čilić	6	6
									Marin Čilić	77	4	6
								5	Taylor Fritz	63	6	4
	5	Taylor Fritz	5	6	6
		Jan-Lennard Struff	7	1	3

Top half

	First round							Second round							Quarterfinals							Semifinals
								1	A Rublev	6	6
		L Đere	3	2					I Ivashka	4	4
		I Ivashka	6	6											1	A Rublev	3	4
	Q	B van de Zandschulp	6	6											Q	B van de Zandschulp	6	6
	Q	Y Nishioka	2	2				Q	B van de Zandschulp	6	7
	WC	N Serdarušić	62	5				8	S Korda	2	5
	8	S Korda	77	7																		Q	B van de Zandschulp	3	3
																							M Čilić	6	6
								3	R Bautista Agut	6	6
	Q	E Gerasimov	5	4					M McDonald	3	2
		M McDonald	7	6											3	R Bautista Agut	4	6	3
		M Čilić	6	6												M Čilić	6	3	6
		A Ramos Viñolas	2	3					M Čilić	6	61	6
		A Mannarino	3	3				6	K Khachanov	4	77	4
	6	K Khachanov	6	6

Bottom half

	First round							Second round							Quarterfinals							Semifinals
	5	T Fritz	6	6
	Q	E Ruusuvuori	1	4				5	T Fritz	77	6
		P Martínez	3	2					T Paul	63	4
		T Paul	6	6											5	T Fritz	6	6
		J Millman	6	6												J Millman	4	2
	WC	Y Oliel	1	1					J Millman	6	6
								4	A Karatsev	3	2
																						5	T Fritz	5	6	6
	7	A Bublik	6	6																			J-L Struff	7	1	3
	WC	E Tiurnev	3	4				7	A Bublik	4	3
		J-L Struff	77	6					J-L Struff	6	6
		J Duckworth	63	3												J-L Struff	6	6
		F Delbonis	2	61											2	D Shapovalov	4	3
	PR	P Andújar	6	77				PR	P Andújar	6	3	0
								2	D Shapovalov	2	6	6

Qualifying

Qualifying draw

First qualifier

	First round							Qualifying competition
	1	Botic van de Zandschulp	6
	Alt	Marc Polmans	6r
								1	Botic van de Zandschulp	5	6	6
								Alt	Evgeny Donskoy	7	3	2
	Alt	Evgeny Donskoy	6	7
	7	Mikael Ymer	2	5

Second qualifier

	First round							Qualifying competition
	2	Benjamin Bonzi	6	64	2
	WC	Dmitry Popko	4	77	6
								WC	Dmitry Popko	62	4
								5	Emil Ruusuvuori	77	6
	PR	Gilles Simon	0	3
	5	Emil Ruusuvuori	6	6

Third qualifier

	First round							Qualifying competition
	3	Federico Coria	3	4
		Radu Albot	6	6
									Radu Albot	62	4
								8	Egor Gerasimov	77	6
		Damir Džumhur	1	66
	8	Egor Gerasimov	6	78

Fourth qualifier

	First round							Qualifying competition
	4	Miomir Kecmanović	2	6	6
	WC	Evgeny Karlovskiy	6	4	1
								4	Miomir Kecmanović	3	6	2
								6	Yoshihito Nishioka	6	4	6
	Alt	Roman Safiullin	5	2
	6	Yoshihito Nishioka	7	6

References

• Main draw
• Qualifying draw