Australian wildcard Kimberly Birrell stunned second seed Emma Navarro on Wednesday while the doubles act of Novak Djokovic and Nick Kyrgios came to a shuddering halt at the Brisbane International.

But it was all smiles from defending men’s champion Grigor Dimitrov, who powered into the quarter-finals in straight sets.

In the opening match on Pat Rafter Arena, Birrell matched world number eight Navarro stroke-for-stroke to put a dent in the American’s Australian Open preparations.

Navarro had a stellar 2024, going deep in all four Grand Slams including a run to the semi-finals of the US Open.

She was expected to brush aside the challenge of 26-year-old Birrell, who has never broken into the top 100 in her 10 years on the WTA Tour.

But the Australian, who trains at the Queensland Tennis Centre and is ranked 113, was not intimidated and delighted her home crowd with a nerveless display. Birrell, who will face 35th-ranked Russian Anastasia Potapova in the last 16, said she embraced the role of underdog.

Dimitrov continued his love affair with Brisbane by easing past another Australian wildcard, Aleksandar Vukic, 6-2, 7-6 (7/5). The Bulgarian world number 10 raced through the first set then held off Vukic as the Australian raised his game in the second.

Djokovic and Kyrgios teamed up for a rare doubles appearance this week, but after winning a close first round were stopped by top seeds Michael Venus of New Zealand and Croatia’s Nikola Mektic 6-2, 3-6, 10/8.

Venus and Mektic came from three points down to clinch the match tiebreak.

Meanwhile, Elena Rybakina’s Kazakhstan dumped defending champions Germany out of the United Cup on Wednesday with world number two Alexander Zverev sidelined by an arm injury barely a week away from the Australian Open.

The upset in Perth sent the Kazakhs into the semi-finals of the 18-nation tournament.

In Sydney, world number two Iga Swiatek led Poland into the last eight by winning a rematch of her 2023 French Open final against the Czech Republic’s Karolina Muchova.

Sixth-ranked Rybakina earned the first point for Kazakhstan, with the 2022 Wimbledon champion hammering Laura Siegemund 6-3, 6-1.

Zverev then withdrew from his clash against Alexander Shevchenko at the last minute with a bicep strain, leaving the 254th-ranked Daniel Masur to face him. He put up a brave fight, but Shevchenko was too strong, powering home 6-7 (5/7), 6-2, 6-2 despite a medical timeout in the second set, complaining about difficulty breathing.

“I was struggling in this heat, it was so rough,” said the world number 78, who upset Stefanos Tsitsipas in group play on Monday.

“I had a headache and my head was spinning. But I wanted to win this one.

“After (losing) the first set, I knew I had to shorten the rallies and play aggressively, tee off on the ball. I just kept pushing after the first set and I’m really happy about it.”

Five-time Grand Slam winner Swiatek scored a battling victory over Muchova, coming out on top 6-3, 6-4 after teammate Hubert Hurkacz was upset in three sets by Tomas Machac.

Swiatek returned to partner Hurkacz and outlast Muchova and Machac in the deciding mixed doubles 7-6 (7/3), 6-3 to keep their tournament alive.

Playing her first event since news broke in late November that she served a one-month ban for a doping violation, Swiatek dropped serve to go 2-1 behind in the first set against Muchova.

But she won the next three games to reassert control and wrapped up the contest comfortably.

“Honestly, I love playing against Karolina because she always brings precision and intensity and a little bit of a different game than most of the girls,” Swiatek said.

“So for sure it’s a challenge. I’m happy that even though I lost my serve when I thought it’s going to be easier, I’m happy that I got my intensity even higher in the last two games to break again.”

Swiatek and Muchova had played three times before and they all went three sets, with the Pole winning two including her memorable Roland Garros triumph.

Agence France-Presse