Naomi Osaka survived a welcome test in her United Cup opener as Japan pushed Great Britain to the brink in Perth, where Emma Raducanu was a late scratching.
The two-time Australian Open champion beat Katie Swan 7-6 (7-4) 6-1 to level their tie at 1-1, before the Brits sealed the rubber in a match tiebreak.
Swan stepped in for Raducanu at late notice and pushed the four-time major winner for almost two hours, before Osaka delivered Japan their first United Cup point in their tournament debut.
Raducanu has been managing a foot injury since the end of last season, but is hopeful she can participate in the United Cup and front up for this month's Australian Open.
"Just fighting, no matter what the score was," Osaka said of what pleased her most about Sunday's victory.
"She was a tough opponent to have as one of the first matches of the year.
"For my confidence - I'm trying to build more - I appreciated winning that first set."
Billy Harris had defeated Shintaro Mochizuki 7-6 (7-4) 6-3 earlier in the day to put Great Britain ahead.
Olivia Nicholls and Neal Skupski then beat Nao Hibino and Yasutaka Uchiyama 7-5 4-6 10-7 for a relieving victory in the deciding mixed doubles.
Earlier, world No.3 Alexander Zverev secured Germany a clinical first-up victory against the Netherlands, beating Tallon Griekspoor 7-5 6-0 in Sydney.
The 2024 tournament champions wasted little time getting on the board, Zverev's win following a 6-2 6-2 victory for compatriot Eva Lys over Suzan Lamens.
Their comprehensive win followed Australia's first-up defeat of Norway on Saturday night, which came despite Alex de Minaur's straight-sets loss to Casper Ruud.
Germany next face Poland, who they beat to claim the title two years ago.
