Del Potro lost to Frank Dancevic in three sets in the second round of the singles at the ATP event in Indianapolis. At the same event, partnered with Travis Parrott in doubles, he won his first doubles tournament, defeating Teymuraz Gabashvili and Karlović in the final. He regards this as a special victory, "It was fantastic to play doubles with Parrott. I'm so happy because I've never won a doubles tournament. For the rest of my life, I will remember this tournament." Del Potro qualified for the ATP Masters Series event in Cincinnati, where he reached the third round. He defeated countryman Guillermo Cañas in the first round and Philipp Kohlschreiber in the second, before losing to former world No. 1 Carlos Moyá. At that year's US Open, he defeated Nicolas Mahut and Melzer, before losing to eventual finalist and third seed Novak Djokovic in the third round. He also reached the third round of the Madrid Masters by beating Potito Starace and Tommy Robredo, before losing to eventual champion David Nalbandian in straight sets. In the last tournament of the year, the Paris Masters, he reached the second round, where he lost to Nikolay Davydenko. That year, del Potro was the youngest player to finish in the year-end top 50 at 19 years, 2 months.