Del Potro qualified for his first US Open in 2006, after being seeded ninth in the qualifying stages, where he beat Brian Vahaly, Wayne Arthurs, and Daniel Köllerer in straight sets. In the US Open, he lost in the first round to fellow qualifier Alejandro Falla of Colombia in four sets. He went on to qualify for his first ATP Masters Series tournament in Spain, the Mutua Madrileña Madrid Open, where he lost in the first round to Joachim Johansson. After receiving a wild card thanks to Roger Federer, he reached the quarterfinals of the 2006 Davidoff Swiss Indoors in Basel, Switzerland; defeating lucky loser Tobias Clemens in the first round and George Bastl in the second round, before losing to the eventual runner-up Fernando González in three sets. Del Potro finished 2006 as the youngest player in the top 100 at 18 years, 2 months.