NEW YORK (Kyodo) -- Japanese ace Kei Nishikori defeated Philipp Kohlschreiber of Germany in straight sets on Monday to reach the quarterfinals of the U.S. Open, the final major of the season.
On a good day all round for Japan, Naomi Osaka reached the last eight of the women's draw after outlasting Aryna Sabalenka of Belarus in three sets at Louis Armstrong Stadium.
It is only the second time that Japan will have players in the quarterfinals of the men's and women's singles competitions. Shuzo Matsuoka and Kimiko Date both reached the last eight of the men's and women's draws, respectively, in 1995.
Nishikori, the 21st seed, surged past Kohlschreiber 6-3, 6-2, 7-5 in 2 hours 16 minutes but admitted the punishing heat had taken its toll.
"I was able to play aggressively during the key moments in the match," said Nishikori, who reached the U.S. Open final in 2014.
"It was a hard match in this heat and my opponent also made mistakes that he doesn't normally make. If I can keep playing like this one match at a time I will have a good chance of progressing further."
Nishikori will play Marin Cilic of Croatia in the quarterfinals.
Osaka, the 20th seed, beat fast-rising Sabalenka 6-3, 2-6, 6-4 in just over two hours to make the quarterfinals of a Grand Slam for the first time. She will face Lesia Tsurenko of Ukraine in the last eight.
"I had a lot of chances to break her (Sabalenka) in the third set," Osaka said. "Then she would serve these really amazing serves. A part of me knew it was coming, but at the same time I was always very unprepared."
"I'm just real glad I was able to win in the end. I was just thinking a little bit negatively of how I would feel if I lost or something."
Osaka was knocked out in the third round in her last two appearances at the U.S. Open in heart-breaking three-setters, first to Madison Keys in 2016, when she led 5-1 in the third set, and then to Kaia Kanepi last summer.
Osaka, whose mother is Japanese and father Haitian, said on court after Monday's win that she would not have forgiven herself if she had suffered defeat this time.
"There's people that call it 'a bad memory' here," she said. "Every time I play a Grand Slam, people ask me am I going to go farther than the third round. Then in Australia I went to the fourth round, then people were like, 'Are you going to go farther than that or is that where you're going to stop?'"
"I've always dreamed of playing here and going to the quarterfinals and farther. So I'm just glad I could do one of my goals."