World No. 22 Naomi Osaka defeated Heather Watson in straight sets Saturday before Kurumi Nara lost her match, giving Japan a 1-1 tie with Britain in their Fed Cup World Group 2 playoff.
Osaka beat the 77th-ranked Watson 6-2, 6-3 in Japan's opening rubber at Bourbon Beans Dome.
She took advantage of her powerful serves and made 11 aces against Watson's two, and did not allow her opponent to convert a single break point before sealing the match in 1 hour, 17 minutes.
"I'm really glad, and just really relieved because I was able to win as this is my first Fed Cup here (in Japan)," Osaka said. "I just really wanted to win and make everyone happy."
Later in the day, Nara, ranked 100th, lost 6-4, 6-2 to No. 23 Johanna Konta in the second singles rubber.
Japan needs to win three of the five matches against Britain to return to World Group 2 for the first time since 2014.
Osaka and Nara will play in Sunday's reverse singles, while Miyu Kato and Makoto Ninomiya face Anna Smith and Gabriella Taylor in the doubles.