Sergi Bruguera defeated Boris Becker in the final, 5–7, 6–4, 7–6^(8–6), 7–6^(7–4) to win the singles tennis title at the 1991 Monte Carlo Open.

Andrei Chesnokov was the defending champion, but lost to Boris Becker in the quarterfinals.^[1]

The top eight seeds received a bye to the second round.

	Quarterfinals							Semifinals							Final
		Magnus Gustafsson	5	5
	9	Sergi Bruguera	7	7
								9	Sergi Bruguera	6	6
									Horst Skoff	1	4
		Horst Skoff	6	6
	6	Jonas Svensson	3	3
															9	Sergi Bruguera	5	6	78	77
															2	Boris Becker	7	4	66	64
	WC	Carl-Uwe Steeb	4	2
		Goran Prpić	6	6
									Goran Prpić	3	3
								2	Boris Becker	6	6
	8	Andrei Chesnokov	1	3
	2	Boris Becker	6	6

	First round							Second round							Third round							Quarterfinals
								1	S Edberg	7	3	63
		M Larsson	6	6					M Larsson	5	6	77
	Q	D Rikl	3	1												M Larsson	62	4
		M Gustafsson	4	6	6											M Gustafsson	77	6
	Q	U Riglewski	6	2	4				M Gustafsson	6	6
	Q	T Tulasne	0	4				15	G Pérez Roldán	4	3
	15	G Pérez Roldán	6	6																			M Gustafsson	5	5
	9	S Bruguera	6	65	6																	9	S Bruguera	7	7
		R Furlan	3	77	3			9	S Bruguera	6	7
		H Leconte	5	6	1				C Caratti	1	5
		C Caratti	7	2	6										9	S Bruguera	6	6
		J Arias	2	66											WC	A Mancini	1	4
	WC	A Mancini	6	78				WC	A Mancini	6	6
								7	E Sánchez	3	3

	First round							Second round							Third round							Quarterfinals
								4	A Agassi	0	77	3
		JP Fleurian	6	4	2				H Skoff	6	63	6
		H Skoff	4	6	6											H Skoff	6	7
		P Lundgren	1	4											Q	C Pistolesi	2	5
		J Aguilera	6	6					J Aguilera	3	6	5
	Q	C Pistolesi	79	5	6			Q	C Pistolesi	6	1	7
	13	M Rosset	67	7	3																		H Skoff	6	6
	11	T Muster	79	2	1																	6	J Svensson	3	3
	Q	V Paloheimo	67	6	6			Q	V Paloheimo	7	6
		M Koevermans	6	6					M Koevermans	5	4
		L Mattar	3	2											Q	V Paloheimo	1	6	3
		F Davín	4	0r											6	J Svensson	6	4	6
	Q	D Pescariu	6	1				Q	D Pescariu	3	6	4
								6	J Svensson	6	4	6

	First round							Second round							Third round							Quarterfinals
								5	G Ivanišević	77	77
		J Arrese	6	6					J Arrese	64	65
	WC	B Borg	2	3											5	G Ivanišević	6	0	2
	WC	T Champion	6	4	3										WC	C-U Steeb	2	6	6
	WC	C-U Steeb	2	6	6			WC	C-U Steeb	6	6
		O Camporese	6	3	6				O Camporese	4	3
	12	A Gómez	3	6	1																	WC	C-U Steeb	4	2
	14	K Nováček	2	4																			G Prpić	6	6
		G Prpić	6	6					G Prpić	6	6
		M Jaite	3	2					R Fromberg	1	4
		R Fromberg	6	6												G Prpić	6	6
		C Bergström	0	2											3	G Forget	2	0
		P Haarhuis	6	6					P Haarhuis	5	4
								3	G Forget	7	6

	First round							Second round							Third round							Quarterfinals
								8	A Chesnokov	77	6
		M Wilander	6	6					M Wilander	63	2
	WC	M Woodforde	0	3											8	A Chesnokov	6	6
		N Kulti	6	63	62										10	A Cherkasov	1	0
		R Agénor	2	77	77				R Agénor	64	3
		E Jelen	0	2				10	A Cherkasov	77	6
	10	A Cherkasov	6	6																		8	A Chesnokov	1	3
	16	A Volkov	5	6	7																	2	B Becker	6	6
		H de la Peña	7	3	5			16	A Volkov	2	6	6
	Q	T Guardiola	3	1					F Santoro	6	1	4
		F Santoro	6	6											16	A Volkov	6	1	1
		M Filippini	1	1											2	B Becker	3	6	6
		J Sánchez	6	6					J Sánchez	77	3	3
								2	B Becker	63	6	6

• 1991 Monte Carlo Open draw