Singles
2021 Croatia Open Umag
Champion	Carlos Alcaraz
Runner-up	Richard Gasquet
Score	6–2, 6–2
Draw	28 (4 Q / 3 WC )
Seeds	8

Carlos Alcaraz defeated Richard Gasquet in the final, 6–2, 6–2 to win the singles tennis title at the 2021 Croatia Open. It was his first ATP Tour title. With the victory, Alcaraz became the youngest player to win an ATP Tour title since Kei Nishikori at the 2008 Delray Beach International Tennis Championships.

Dušan Lajović was the reigning champion from when the tournament was last held in 2019, but lost to Daniel Altmaier in the quarterfinals.

Seeds

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

Draw

Finals

	Semifinals							Final
	1	Albert Ramos Viñolas	2	63
	7	Carlos Alcaraz	6	77
								7	Carlos Alcaraz	6	6
								4	Richard Gasquet	2	2
	4	Richard Gasquet	77	3	6
	Q	Daniel Altmaier	62	6	3

Top half

	First round							Second round							Quarterfinals							Semifinals
								1	A Ramos Viñolas	7	6
	Q	A Collarini	3	2				WC	D Ajduković	5	4
	WC	D Ajduković	6	6											1	A Ramos Viñolas	6	6
		C Taberner	6	6												S Travaglia	2	1
	WC	N Serdarušić	2	2					C Taberner	4	3
		S Travaglia	6	77					S Travaglia	6	6
	6	J Munar	3	61																		1	A Ramos Viñolas	2	63
																						7	C Alcaraz	6	77
								3	F Krajinović	6	6
	WC	H Rune	6	3	2				R Albot	4	2
		R Albot	1	6	6										3	F Krajinović	63	6	1
	LL	R Olivo	6	2	61										7	C Alcaraz	77	2	6
		A Martin	1	6	77				A Martin	3	1
		L Pouille	6	2	2			7	C Alcaraz	6	6
	7	C Alcaraz	3	6	6

Bottom half

	First round							Second round							Quarterfinals							Semifinals
	5	A Bedene	1	4
		M Cecchinato	6	6					M Cecchinato	3	1
		D Džumhur	6	6					D Džumhur	6	6
	Q	F Horanský	4	3												D Džumhur	3	67
	Q	A Giannessi	77	7											4	R Gasquet	6	79
		J Veselý	64	5				Q	A Giannessi	64	4
								4	R Gasquet	77	6
																						4	R Gasquet	77	3	6
	8	G Mager	0	6	6																	Q	D Altmaier	62	6	3
		P Martínez	6	3	3			8	G Mager	6	1	5
	Q	D Altmaier	5	6	0			Q	D Altmaier	4	6	7
		C Moutet	7	1	0r										Q	D Altmaier	6	6
		B Zapata Miralles	4	6	6										2	D Lajović	2	4
		P Cuevas	6	2	4				B Zapata Miralles	5	4
								2	D Lajović	7	6

Qualifying

Qualifying draw

First qualifier

	First round							Qualifying competition
	1	Daniel Altmaier	2	6	6
	Alt	Flavio Cobolli	6	3	1
								1	Daniel Altmaier	3	6	6
								WC	Matija Pecotić	6	4	3
	WC	Matija Pecotić	7	6
	7	Thomas Fabbiano	5	2

Second qualifier

	First round							Qualifying competition
	2	Nikola Milojević	6	7
		Lukáš Rosol	4	5
								2	Nikola Milojević	2	2
								5	Filip Horanský	6	6
	WC	Hamad Međedović	4	77	1
	5	Filip Horanský	6	62	6

Third qualifier

	First round							Qualifying competition
	3	Blaž Rola	4	2
		Vitaliy Sachko	6	6
									Vitaliy Sachko	77	2	4
									Andrea Collarini	64	6	6
		Andrea Collarini	6	6
	8	Daniel Masur	1	1

Fourth qualifier

	First round							Qualifying competition
	4	Alessandro Giannessi	6	7
		Rudolf Molleker	3	5
								4	Alessandro Giannessi	77	6
								6	Renzo Olivo	65	1
	Alt	Nerman Fatić	3	1
	6	Renzo Olivo	6	6

References

• Main draw
• Qualifying draw