At the AIG Japan Open Tennis Championships, he made the final by defeating 11th seed Jarkko Nieminen, top seed and defending champion Ferrer, and fourth seed Richard Gasquet. He was defeated by Tomáš Berdych in the final. At the Madrid Masters, he lost in the quarterfinals in straight sets to Roger Federer. He reached the semifinals of his next tournament, the Davidoff Swiss Indoors, before losing to countryman Nalbandian. He was beaten by Nalbandian again in his next tournament, this time it was in the second round of the Paris Masters. Del Potro blamed fatigue for his defeat, "It's difficult to play the last tournament of the year. I was tired, my mind was in Argentina 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.