PERTH: 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 event in Perth and Sydney 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. 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 track to win 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.” World number two Iga Swiatek, playing her first match since a month-long ban for a doping breach ended on Dec 4, got Poland off to a blazing start against Norway in Group B by beating Malene Helgo 6-1, 6-0. Casper Ruud cancelled out their advantage by seeing off Hubert Hurkacz 7-5, 6-3. Poland were not to be denied, however, as Swiatek and Jan Zielinski overcame Ruud and Ulrikke Eikeri 6-3, 0-6 (10-8). Earlier in Sydney, Katie Boulter and Charles Broom guided Britain to a 2-1 win over Argentina in Group ‘F’, winning their mixed doubles clash with 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. Defending champions Germany edged past China 2-1 to top Group E and book a meeting with Kazakhstan in the quarter-finals after Alexander Zverev and Laura Siegemund beat Zhang and Zhang Shuai 6-2, 7-6(3). Zverev rallied to a 2-6, 6-0, 6-2 victory over Zhang Zhizhen before Gao Xinyu beat Siegemund 6-1, 3-6, 6-3 with the two results sending both teams into the knockout stage.