Japanese world No. 9 Kei Nishikori crashed out of the Italian Open on Thursday as he suffered a 7-6(4), 6-3 defeat to Argentina's Juan Martin del Potro in the third round of the men's singles.

The seventh-seeded Nishikori, coming back from a right wrist injury, lost the opening set in a tiebreaker after struggling with his first serve, a main factor in his straight-sets victory over Spain's David Ferrer in the second round.

In the round of 16 match at the Foro Italico in Rome that lasted 1 hour, 54 minutes, Nishikori failed to generate a single breakpoint chance in the second set as he saw his first serve percentage drop to 58 percent compared to 75 percent in the second round.

Del Potro, the 2009 U.S. Open champion who currently ranks 34th in the world, recorded eight aces and improved his head-to-head against Nishikori to 5-1, his only loss coming at the indoor tournament in Switzerland last fall.

"Most of my shots were shallow. It wasn't my worst game but I could've played better in some situations. It didn't go as expected," said Nishikori.

"I wasn't able to win key points. I lacked confidence."

Del Potro set up a quarterfinal clash with world no. 2 Novak Djokovic of Serbia, while world no. 4 Rafael Nadal of Spain meets seventh-ranked Dominic Thiem of Austria in another last-eight match.

Nishikori is scheduled to compete in the French Open which gets under way May 28 in Paris, but finds himself in a tight spot as he saw his plans to bounce back from injury and regain top form before the Grand Slam event go up in smoke after Thursday's loss.

"I have to raise my level of play, or I won't be able to advance in the French Open," he said.

Meanwhile, the Japanese women's doubles pair of Eri Hozumi and Miyu Kato was defeated by the U.S.-Slovenia duo of Abigail Spears and Katarina Srebotnik 6-2, 7-5 in the second round.