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.