Defending champ Nadal limps out of U.S. Open

NEW YORK — Rafael Nadal felt the pain sear into his right knee early in his U.S. Open semifinal, on what he called “a bad movement.” It was a familiar pain, one that he has dealt with off-and-on for years.

The defending champion looked up at his guest box and indicated something was wrong. He tried to continue. Eventually, he could not.

Nadal stopped playing after dropping the opening two sets Friday night, putting Juan Martin del Potro back in a Grand Slam final for the first time since winning the 2009 title at Flushing Meadows.

“That was not a tennis match at the end. Just one player playing, the other staying on one side of the court,” Nadal said. “I hate to retire, but staying one more set out there, playing like this, would be too much for me.”

On Sunday, No. 3 del Potro will face No. 6 Novak Djokovic, who advanced with an emphatic 6-3, 6-4, 6-2 victory over No. 21 Kei Nishikori in the second semifinal.

“I don’t know how it looked, but it felt really good,” said Djokovic, who reached his record-tying eighth final in New York as he aims for a third U.S. Open championship and 14th major title. “Great intensity, great focus, good game plan. Obviously easier said than done. You have to execute the shots.”

Del Potro was leading 7-6 (3), 6-2 after two hours of play when Nadal shook his head and said he had to retire, becoming the first man in the half-century professional era to do so during a semifinal or final at the U.S. Open.