difficult to play the last tournament of the year. I was tired, my mind was in Argentina [the venue for the Davis Cup final]". This left del Potro's qualification for the 2008 Tennis Masters Cup out of his hands, but Jo-Wilfried Tsonga beat James Blake in the semifinals, which was enough to ensure his place at the year-end event. Del Potro won one match at the Masters Cup, against Tsonga, but lost his other two matches against the higher-ranked Djokovic and Davydenko, meaning that he exited the tournament in the round-robin stage. This was his last event of the year on the ATP Tour. He went on to lose one match in the Davis Cup final, against López, as his team succumbed to a 3–1 loss against Spain. He withdrew from his second match due to a thigh injury and was replaced by José Acasuso. Nonetheless, del Potro enjoyed a successful season; winning four titles and finishing 2008 as the youngest player in the top 10, top-ranked Argentine, and highest-ranked South American. 2009: US Open champion, Year-End Finals final, top 5 Del Potro began his 2009 season at the Heineken Open in Auckland, New Zealand, del Potro was the top seed. He defeated American Sam Querrey in the final to win the title, the fifth of his career. Seeded eighth at the Australian Open, he beat Marin Čilić in the fourth round. Del Potro's tournament ended in his next match, when he lost in straight sets to Federer. At the BNP Paribas Open, the sixth seed del Potro advanced to the quarterfinals, where he was defeated by world No. 1 Nadal. Del Potro avenged that loss the following week at the Sony Ericsson Open, where he came back from a double break down in the third set at 0–3 to defeat Nadal in the quarterfinals. This was the first time del Potro had defeated Nadal in five meetings. Despite a loss in the semifinals to Murray, del Potro reached a career-high world ranking of No. 5. In the clay-court season, del Potro was eliminated in the second round of the Monte Carlo Masters by Ivan Ljubičić. In Rome, del Potro beat Victor Troicki and Wawrinka to advance to the quarterfinals, where he was defeated by defending champion Djokovic in straight sets. This meant del Potro's head-to-head record with the Serb was now 0–3. Del Potro then played at the 2009