Félix Mantilla defeated Roger Federer in the final, 7–5, 6–2, 7–6^(10–8) to win the men's singles tennis title at the 2003 Italian Open.

Andre Agassi was the defending champion, but lost in the first round to David Ferrer.

A champion seed is indicated in bold text while text in italics indicates the round in which that seed was eliminated.

	Quarterfinals							Semifinals							Final
		Ivan Ljubičić	6	3	4
		Félix Mantilla	3	6	6
									Félix Mantilla	4	77	6
									Yevgeny Kafelnikov	6	63	4
		Yevgeny Kafelnikov	6	7
	Q	Martin Verkerk	3	5
																Félix Mantilla	7	6	710
															4	Roger Federer	5	2	68
	WC	Filippo Volandri	3	7	2
	4	Roger Federer	6	5	6
								4	Roger Federer	6	4
								2	Juan Carlos Ferrero	2	2r
	12	Rainer Schüttler	4	4
	2	Juan Carlos Ferrero	6	6

	First round							Second round							Third round							Quarterfinals
	1	A Agassi	6	63	4
		D Ferrer	0	77	6				D Ferrer	2	3
		I Ljubičić	6	6					I Ljubičić	6	6
		X Malisse	2	4												I Ljubičić	6	6
	Q	V Hănescu	77	6											15	G Coria	4	3
		M Youzhny	61	3				Q	V Hănescu	1	66
		T Henman	2	1				15	G Coria	6	78
	15	G Coria	6	6																			I Ljubičić	6	3	4
	11	D Nalbandian	3	6	0																		F Mantilla	3	6	6
		F Mantilla	6	1	6				F Mantilla	6	6
		M Fish	7	7					M Fish	4	3
		F Santoro	5	5												F Mantilla	7	4	6
	WC	D Sanguinetti	1	3											7	A Costa	5	6	1
		A Clément	6	6					A Clément	77	2	4
	Q	Ž Krajan	4	5				7	A Costa	63	6	6
	7	A Costa	6	7

	First round							Second round							Third round							Quarterfinals
	3	C Moyá	6	6
		F Vicente	2	4				3	C Moyá	6	6
		N Lapentti	6	63	3				M Mirnyi	4	4
		M Mirnyi	4	77	6										3	C Moyá	4	64
		B Vahaly	5	6	3											Y Kafelnikov	6	77
	WC	G Galimberti	7	4	6			WC	G Galimberti	5	1
		Y Kafelnikov	6	1	6				Y Kafelnikov	7	6
	16	Y El Aynaoui	1	6	4																		Y Kafelnikov	6	7
	9	P Srichaphan	1	2																		Q	M Verkerk	3	5
		J Nieminen	6	6					J Nieminen	7	4	6
		N Davydenko	2	6	7				N Davydenko	5	6	1
		K Kučera	6	1	5											J Nieminen	0	3
	Q	M Verkerk	6	77											Q	M Verkerk	6	6
		V Spadea	3	62				Q	M Verkerk	66	6	6
	WC	A Gaudenzi	2	3				5	A Roddick	78	3	4
	5	A Roddick	6	6

	First round							Second round							Third round							Quarterfinals
	LL	N Massú	6	2	1
	WC	F Volandri	1	6	6			WC	F Volandri	6	7
		R Sluiter	6	4	6				R Sluiter	1	5
		J-M Gambill	4	6	2										WC	F Volandri	6	6
		R Štěpánek	6	1	6											R Štěpánek	3	4
		J Blake	2	6	3				R Štěpánek	6	6
	Q	A Martín	2	6	6			Q	A Martín	4	3
	10	S Schalken	6	3	1																	WC	F Volandri	3	7	2
	13	S Grosjean	77	4	3																	4	R Federer	6	5	6
		T Robredo	64	6	6				T Robredo	6	6
		J I Chela	6	6					J I Chela	2	0
		O Rochus	1	1												T Robredo	1	1
		M Zabaleta	6	6											4	R Federer	6	6
		D Sánchez	4	2					M Zabaleta	64	2
		P-H Mathieu	3	5				4	R Federer	77	6
	4	R Federer	6	7

	First round							Second round							Third round							Quarterfinals
	8	J Novák	6	6
		W Arthurs	3	3				8	J Novák	6	6
		D Hrbatý	6	6					D Hrbatý	1	4
	Q	T Enqvist	3	3											8	J Novák	4	62
		W Ferreira	3	6	6										12	R Schüttler	6	77
		F López	6	4	3				W Ferreira	64	2
	Q	M Norman	67	5				12	R Schüttler	77	6
	12	R Schüttler	79	7																		12	R Schüttler	4	4
	14	G Kuerten	3	6	4																	2	J C Ferrero	6	6
		G Gaudio	6	2	6				G Gaudio	6	6
		A Calleri	6	6					A Calleri	4	2
		S Koubek	2	2												G Gaudio	7	0	2
	Q	A Portas	6	2	2										2	J C Ferrero	5	6	6
		À Corretja	3	6	6				À Corretja	4	4
	Q	M Philippoussis	63	4				2	J C Ferrero	6	6
	2	J C Ferrero	77	6

• 2003 Internazionali BNL d'Italia Singles draw
• 2003 Internazionali BNL d'Italia Qualifying draw