World number six Rybakina makes winning start at United Cup
The All England Club winner from 2022 clinched the opening tie of the 18-nation ATP-WTA event, which begins the 2025 year in Perth and Sydney.
Each team features three men and three women, with ties comprising one men's and one women's singles and an often decisive mixed-doubles clash.
Rybakina and Alexander Shevchenko produced a 7-6 (7/4), 6-7 (2/7), 10-7 result over Spaniards Pablo Carreno Busta and Yvonne Cavalle-Reimers in the mixed doubles to earn the win.
"It was a really tough one, first matches are always difficult," Rybakina said. "It's not easy to get used to it that quick, but I'm really happy with the way I played today."
Rybakina, who won three titles in her first eight tournaments last season before being sidelined by injuries and illness, secured the first point for the Kazakhs, defeating Jessica Bouzas Maneiro 6-2, 6-3 in their singles rubber.
Shevchenko was unable to overcome the 33-year-old Carreno Busta in his singles match to seal the tie, losing 6-2, 6-1 and throwing the session into the deciding mixed doubles.
The outcome remained in doubt until the end, with Rybakina duelling with the Spaniards before Shevchenko ended the drama with a winning volley at the net after 82 minutes.
Shevchenko praised his Grand Slam champion teammate for "carrying me", while Rybakina credited his fighting spirit for getting the job done in the final set.
China face Brazil in the night session in Perth, with the action in Sydney starting on Saturday.