NEW YORK (Kyodo) -- Japan's Kei Nishikori suffered a straight sets loss Friday against former world No. 1 Novak Djokovic of Serbia and made a semifinal exit at the U.S. Open.
Nishikori was handed a swift defeat at Arthur Ashe Stadium, losing 6-3, 6-4, 6-2 to the sixth seed. He took his 14th straight loss against the Serbian, a two-time U.S. Open winner who now boasts a 15-2 record against the Japanese.
"Today I couldn't play like myself," Nishikori said. "There were moments when I couldn't keep up with (Djokovic's) level and get my feet moving."
"These last two weeks I've played good tennis and I think I'm just worn out," he said.
Nishikori, who outlasted Cilic in a four-hour marathon Wednesday, led briefly in the second and third sets but looked sluggish against an unrelenting Djokovic. Nishikori committed 51 unforced errors in the 2 hour, 22 minute match.
"I thought I came out of the block with a great intensity and a great focus," Djokovic said. "You have to execute the shots against Kei Nishikori, who is one of the quickest movers on the tour and takes away a lot of your time."
The 28-year-old Japanese was looking to make his second appearance in a Grand Slam final. He beat Djokovic in the 2014 U.S. Open semifinals but was swept away by Croatian Marin Cilic in the title match.
Despite having his solid run at the season's final Grand Slam ended, Nishikori said he looks forward to his next match with Djokovic.
"His (Djokovic) defining trait is his tenacity," Nishikori said. "Today I couldn't hit decisively and that killed me. Matches against him are a chance to get better, so I look forward to them. I'll take home today's defeat as a lesson."
Djokovic, who is chasing back-to-back Grand Slam victories after winning Wimbledon in July, will face Juan Martin del Potro in the men's final. The No. 3 Argentinian advanced after defending champion Rafael Nadal retired from Friday's other semifinal with a knee injury.
Nishikori will be rooting for his younger compatriot, Naomi Osaka, when the 20-year-old lives out her childhood dream and faces 23-time major winner Serena Williams in the women's singles final.
"I think she has a chance to beat Serena," Nishikori said. "The final is different to the semis, but I just want her to have fun playing good tennis."
Osaka made history by becoming the first Japanese woman to reach a Grand Slam final when she beat American Madison Keys in the semifinals on Thursday.