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2004: Davis Cup title

2004 started with a doubles title alongside Tommy Robredo at the Chennai Open, defeating Israeli pair Jonathan Erlich and Andy Ram in the final; Nadal's second doubles title and first on hard courts. In singles, however, Nadal piled up his 5th consecutive loss after a first round exit to Thierry Ascione; this remains the worst losing streak of his career. He bounced back in the very next tournament in Auckland as he reached the first ATP final of his career, which he lost to Dominik Hrbatý. Nadal then reached the third round of the Australian Open, where he lost in straight sets to former world No. 1 and Australian native Lleyton Hewitt. Later that year, Nadal, then ranked No. 34, played the first match of his historic rivalry with Roger Federer, then ranked No. 1, in the third round of the Miami Open, winning in straight sets before a loss to Fernando González in the fourth round.

In the first tournament of the clay court season at Estoril, Nadal suffered a stress fracture in his left ankle during his round of 16 victory over Richard Gasquet, causing him to miss 3 months of play and 2 majors, the French Open and Wimbledon. On his return in July, he struggled to regain his form, and although he won his first ATP singles title at the Prokom Open by defeating No. 105 José Acasuso in the final, Nadal won hardly any other match on the tour. At the US Open, Nadal lost to defending champion Andy Roddick in the second round, but he also entered the tournament's doubles event partnering Robredo, where they upset the No. 4 seed in the third round and reached the semi-finals; Nadal's best performance in a grand slam doubles event.

In the 2004 Davis Cup final, the 18-year-old Nadal beat world No. 2 Andy Roddick on clay in Spain to help his nation clinch the title over the United States, and in doing so at 18 years and six months of age, he became the youngest player to register a singles victory in a Davis Cup final for a winning nation. Nadal finished the year ranked as the world No. 51, two places worse than the prior year, mainly because he missed most of the clay court season.