Earlier, Karen Khachanov and Anastasia Pavlyuchenkova beat Yuichi Sugita and Naomi Osaka 4-1, 4-0 in a Fast4 mixed doubles decider to give Russia a 2-1 victory over Japan.
The Russian team took advantage of a number of unforced errors by Sugita and Osaka in the Fast4 format, which includes four-game sets, five-point tiebreakers, no advantage and no let scoring.
In singles, Khachanov beat Sugita 6-4, 6-2 after Osaka overcame illness to beat 15th-ranked Pavlyuchenkova 6-4, 3-6, 7-6 (5).
After not being able to play at all against the U.S. on Tuesday, Osaka required assistance from a doctor during the second set Thursday but was able to continue to beat the Russian player.
"I just feel like to play like that against someone so well, and not be 100 percent and still win, I should be proud of myself," Osaka said.
Pavlyuchenkova leaves Perth without a singles victory. The 2017 Australian Open quarterfinalist also lost to Switzerland's Belinda Bencic and then CoCo Vandeweghe of the U.S.