2021 Open de Oeiras IV – Singles

Carlos Alcaraz was the defending champion^[1] but chose not to defend his title.

Singles
2021 Open de Oeiras IV
Champion	Gastão Elias
Runner-up	Holger Rune
Score	5–7, 6–4, 6–4

Main article: 2021 Open de Oeiras IV

Gastão Elias won the title after defeating Holger Rune 5–7, 6–4, 6–4 in the final.

Seeds

1. Mathias Bourgue (first round)
2. Wu Tung-lin (second round)
3. Julian Lenz (second round)
4. Tseng Chun-hsin (second round)
5. Roberto Quiroz (first round)
6. Carlos Gimeno Valero (quarterfinals)
7. Pedro Cachin (first round)
8. Riccardo Bonadio (second round)

Draw

Key

• Q = Qualifier
• WC = Wild card
• LL = Lucky loser
• Alt = Alternate
• ITF = ITF entry
• PR = Protected ranking
• SR = Special ranking
• SE = Special exempt
• JE = Junior exempt
• JR = Junior Accelerator Programme entrant
• CO = College Accelerator Programme entrant
• NG = Next Gen Accelerator Program entrant
• w/o = Walkover
• r = Retired
• d = Defaulted

Finals

	Semifinals							Final
		Gastão Elias	4	7	0
		Nuno Borges	6	5	0r
									Gastão Elias	5	6	6
									Holger Rune	7	4	4
		Holger Rune	6	3	6
	Q	Timofey Skatov	2	6	2

Top half

	First round							Second round							Quarterfinals							Semifinals
	1	M Bourgue	2	2
	WC	Pedro Araújo	6	6				WC	P Araújo	5	0
		G Elias	6	6					G Elias	7	6
	WC	Luís Faria	2	3												G Elias	60	6	6
		C Ugo Carabelli	6	6												C Ugo Carabelli	77	3	0
		J de Jong	4	2					C Ugo Carabelli	4	7	6
		J Forejtek	64	6	0			8	R Bonadio	6	5	4
	8	R Bonadio	77	3	6																		G Elias	4	7	0
	4	C-h Tseng	6	6																			N Borges	6	5	0r
		R Ortega Olmedo	4	2				4	C-h Tseng	3	6	1
		J Härteis	3	0				Q	FC Jianu	6	3	6
	Q	FC Jianu	6	6											Q	FC Jianu	4	4
		N Serdarušić	4	5												N Borges	6	6
	Q	D Yevseyev	6	7				Q	D Yevseyev	77	4	2
		N Borges	6	6					N Borges	62	6	6
	5	R Quiroz	3	0

Bottom half

	First round							Second round							Quarterfinals							Semifinals
	6	C Gimeno Valero	6	6
		V Sachko	2	1				6	C Gimeno Valero	6	6
	PR	V Galović	4	77	6			PR	V Galović	4	2
		D Ajduković	6	64	1										6	C Gimeno Valero	2	4
		H Rune	6	6												H Rune	6	6
		T van Rijthoven	3	4					H Rune	5	6	6
	Alt	C Denolly	4	0				3	J Lenz	7	4	3
	3	J Lenz	6	6																			H Rune	6	3	6
	7	P Cachin	4	7	61																	Q	T Skatov	2	6	2
		G Oliveira	6	5	77				G Oliveira	3	1
		I Sijsling	6	2	64			Q	T Skatov	6	6
	Q	T Skatov	2	6	77										Q	T Skatov	77	5	6
		G Blancaneaux	3	2											Q	N Sánchez Izquierdo	64	7	1
	Q	N Sánchez Izquierdo	6	6				Q	N Sánchez Izquierdo	6	77
	WC	T Cação	1	1				2	T-l Wu	2	62
	2	T-l Wu	6	6