He fell early at the third round of the Canada Masters to Karol Kučera 3–6, 5–7 and at the second round of the Western & Southern Financial Group Masters to Gastón Gaudio 7–6(7–3), 6–7(5–7), 4–6. At the 2003 US Open his good form at the Grand Slams continued, eliminating former world No. 1s and former US Open champions Lleyton Hewitt 4–6, 6–3, 7–6(7–5), 6–1 and Andre Agassi 6–4, 6–3, 3–6, 6–4, before losing to Andy Roddick, 3–6, 6–7(2–7), 3–6, in the final. This result saw Ferrero take the No. 1 ranking from Agassi. He once again represented Davis Cup this time against Argentina, defeating Gastón Gaudio 6–4, 6–0, 6–0 but losing to Agustín Calleri 4–6, 5–7, 1–6. The year continued in Bangkok where he played for the first time as No. 1, losing to Taylor Dent in the final, 3–6, 6–7. He took his next title at the Madrid Masters, his first hard–court Masters title, by defeating Nicolás Massú, 6–3, 6–4, 6–3, in the final. He was presented with the Spanish "National Sportsman of the Year" award from King Juan Carlos. However, he went into a 6 match losing streak, In the third round of the BNP Paribas Masters to Jiří Novák 5–7, 5–7. At the Tennis Masters Cup, he lost all his three matches against David Nalbandian, Andre Agassi, and Roger Federer. Representing Spain in the Davis Cup final against Australia, he lost both his matches in 5 sets against Lleyton Hewitt 6–3, 3–6, 6–3, 6–7(0–7), 2–6 and Mark Philippoussis 5–7, 3–6, 6–1, 6–2, 0–6. Ferrero ended the year ranked No. 3, behind Andy Roddick and Roger Federer.