Kazakhstan reached the quarter-finals of the United Cup mixed team tournament with a comfortable win over Greece on Monday as Elena Rybakina defeated Maria Sakkari 6-4 6-3 after Alexander Shevchenko stunned Stefanos Tsitsipas.
Former Wimbledon champion Rybakina, who is using the 18-nation tournament to prepare for next month's Australian Open, edged a tight opening set against Sakkari before powering ahead 5-0 in the next.
She was broken late on but stayed composed to close out the contest on serve, leaving her new coach Goran Ivanisevic beaming in the dugout.
"We've just been working a couple weeks together. This is our first official tournament," Rybakina said.
"We're still getting to know each other a bit. He's a fun guy. He gives some experience from when he played and also as a coach. I'm just happy to work with him.
"Hopefully we'll have some good results together."
Shevchenko pulled off a major upset earlier when he downed an ill and error-prone world number 11 Tsitsipas 6-4 7-6(0) to put Kazakhstan on course for victory in the Group C tie in Perth.
"It will definitely go in my record as one of my best wins," Shevchenko said.
"He wasn't at his best today but still I played really well and I found the moments to win the match."
In Sydney, Katie Boulter and Charles Broom guided Britain to a 2-1 win over Argentina in Group F, winning their mixed doubles rubber against Maria Lourdes Carle and Tomas Martin Etcheverry 7-6(4) 7-5.
Boulter put Britain up 1-0 with a 6-2 6-3 win over Nadia Podoroska but Argentina fought back immediately as Etcheverry overcame a stomach issue to down Billy Harris 3-6 6-3 6-2.
World number two Iga Swiatek will be in action when Poland face Norway in Group B, while defending champions Germany meet China in Group E.
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