Dominic Thiem says he found it difficult to bounce back from his defeat to Juan Martin del Potro at the US Open.

The Austrian was up two sets before del Potro shrugged off apparent illness to win their fourth round encounter in five sets.

Speaking to Sky Sports Austria, Thiem reviewed a season in which he has reached a career-high No. 6 in the rankings and his first Grand Slam semifinal at the French Open.

"There were some positive highlights, but negative also," he said. "The claycourt season was exceptionally good—I reached all my goals and won a title. On grass, I played better than previous years. The negative highlight of the season was the US Open, where I was playing very good, and that very tight match to del Potro was very painful."

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Though he got two Davis Cup wins against sub-600 ranked opponents, Thiem did not win a match in his next three ATP events and fell to Richard Gasquet at his home event in Vienna this week.

"I took too long a break, and the defeat gnawed at me," he said. "It cost me a lot—a Top 5 ranking, a quarterfinal against Federer. On the other hand, del Potro beat Federer and now is playing very good, which means it was a very good match."

Thiem is now scheduled to play next week's event at Paris, and has clinched a spot at the ATP Tour Finals.

"I'm happy I could qualify," he said. "My goal is to finish the season with good play and good feelings."