When Shuzo Matsuoka and Kimiko Date reached the men’s and women’s quarterfinals at Wimbledon in 1995, it was a fluke ? at least in the eyes of one of them.

On Wednesday night in the players’ garden adjacent to Arthur Ashe Stadium, Matsuoka reflected on his accomplishment from decades ago in light of the momentous events that had just taken place inside the arena next to him.

Kei Nishikori, a player who at 12 was coached by Matsuoka in Japan, and Naomi Osaka had both won their quarterfinal matches to become the first Japanese duo to reach the semifinals of the same Grand Slam tournament.

Nishikori and Osaka had already become the first two Japanese players just to reach the quarterfinals at the same major event since Matsuoka and Date did it 23 years ago.

“But there is a big difference,” Matsuoka said. “I was so lucky to get to the quarterfinals at Wimbledon. But these two can do big things. They can actually win Grand Slams.”

Osaka and Nishikori took a significant step closer with a pair of impressive victories. Osaka, an endearing 20-year-old who was born in Japan but grew up in the United States, rolled past unseeded Lesia Tsurenko of Ukraine, 6-1, 6-1, in just 57 minutes to reach her first Grand Slam semifinal. The 20th-seeded Osaka will play No. 14 Madison Keys, who beat Carla Suarez Navarro, 6-4, 6-3, in a quarterfinal on Wednesday.

Nishikori, the No. 21 seed on the men’s side, took four times as long in his match on the same court, but overcame a shaky first set to upset No. 7 Marin Cilic of Croatia, 2-6, 6-4, 7-6 (5), 4-6, 6-4, in a rematch of their 2014 final here. In the semifinals, Nishikori will face No. 7 Novak Djokovic, who rolled to a straight-sets victory over John Millman late Wednesday.

According to Matsuoka, who is commenting at the Open for a Japanese television network, both semifinals will draw intense interest in Japan, a nation recognized more for producing baseball, soccer and sumo wrestling stars than for developing champion tennis players.

Nishikori, 28, has come closest, reaching the U.S. Open final in 2014 and the semifinal stage here in 2016. He noted the growing interest around the grounds from Japanese fans and reporters energized to see two of their compatriots this deep in a major event.

“I saw a lot of Japanese coming up for the tournament,” Nishikori said. “It’s good to have the home support outside of Japan. It’s great news we are both in semis.”

Along with the breakthroughs on court, the two have also made a breakthrough in their relationship. Both players train in Florida, albeit on different coasts, but both are generally shy, and Osaka said she had finally gotten to know Nishikori personally at this tournament. They were both at a late-night dinner in Rome in May, but Osaka said she was tired and incommunicative that time.

Here, she surprised Nishikori when she began chatting with him on the grounds, mostly about typical young-adult topics, like video games.

“I just think he’s, like, a really big kid,” Osaka said. “Like, I don’t know how to describe it. He plays games and stuff, too. I think we’re pretty similar in that sense. Overall, he’s just really nice and positive and bubbly and stuff.”

Nishikori had a similar impression of Osaka.

“Well, she looks mature and she looks older,” he said. “But when we talk, she’s also a kid.”

But the kid has had a breakout year, underscoring Matsuoka’s belief that she, along with Nishikori, can win a Grand Slam. Osaka won in Indian Wells, Calif., for her first WTA tour championship, beating No. 1 Simona Halep along the way. At the next tournament in Miami, she demonstrated a steely nerve by beating her idol, Serena Williams.

Until this U.S. Open, Osaka’s best showing at a Grand Slam tournament was reaching the fourth round at the Australian Open this year.

But as she has steadily progressed, especially this year under the tutelage of Sascha Bajin, Williams’s former coach, Osaka has added an emotional and tactical awareness to her already impressive power game. As her results have improved, so too has her stature in Japan.

“Naomi is coming, and the good thing is she has a good character, a very cute character,” Matsuoka said. “She is very, very funny, and in Japan, everyone is starting to like her. They didn’t know about Naomi, how she is on the inside. Now they know this.”

Born in Japan to a Japanese mother from Hokkaido and a Haitian-American father, Osaka moved to Long Island with her family when she was 3, and then five years later moved to Florida to train more seriously. She holds dual citizenship from Japan and the United States, but she chose to represent Japan after she was overlooked by the United States Tennis Association as a developing junior player.

She knew only rudimentary Japanese growing up, but in recent years she began to study the language. She can now understand questions posed to her in Japanese (she answers in English to avoid mistakes) from the growing ranks of reporters from Japan who follow her around the world.

“I’m really grateful that I get a lot of Japanese press,” Osaka said. “I think it’s because of Kei. I’m really happy about that. I just hope that I can keep doing well. I hope that they keep cheering for me.”