Zhuhai/Wuhan: Top seed Stefanos Tsitsipas had trouble breathing and quit his opening match at the Zhuhai Championships on Thursday after calling a medical time-out before the deciding set.The 21-year-old Greek was the strong favourite against unseeded Adrian Mannarino of France and took the first set 6-3 in southern China. But he appeared to labour badly after that, bending over several times on court and putting his hands on his knees.He was far from his best as he lost the second set 7-5, and retired soon after, looking red in the face and burying his head in his hands.Tournament officials said that he had been having problems breathing and was getting medical attention, but did not go to hospital.BARTY PARTYAshleigh Barty marched into her sixth semi-final of the season Thursday, describing her victory over Petra Martic in Wuhan as one of the best matches she’s played in recent times.The world number one impressed in a highly entertaining quarter-final that saw her fire 39 winners en route to a 7-6 (8/6), 3-6, 6-3 win against Martic.Barty now gets a shot at revenge when she takes on powerful Belarusian Aryna Sabalenka on Friday in a rematch of their Wuhan semi-final last year.Against Martic, Barty fell behind early in the first and third sets, but retaliated with some creative shot-making to reach the last four for a third year in a row.”I think that was a very, very high-quality match. I think that was probably one of the better matches that I’ve played in recent times,” said the reigning French Open champion.”It could have gone either way. I was happy how I was able to fight in the end, put a lot of pressure on her in a lot of those service games in the third.”Martic, the world number 22 from Croatia, had not lost a three-setter since March, but saw her streak of 16 on-the-trot snapped by the relentless Barty.”She’s one of the best movers on the tour,” Barty said of Martic. “That (streak) doesn’t surprise me.”Sabalenka, the defending champion and seeded nine this week, overcame a second-set dip to halt the inspired run of Kazakh wildcard Elena Rybakina 6-3, 1-6, 6-1 on Thursday.The 21-year-old is tied at 2-2 in her head-to-head with Barty.Sabalenka improved her strong career record on Chinese courts to 27 wins against just six losses — including 10 victories on the trot in Wuhan.”I just feel that I am thinking clean and I am moving much better,” said Sabalenka, who is enjoying a resurgence this month after struggling to adapt to her rapid rise earlier in the year.”That’s what we’ve been working on. Takes a little while.”Two-time champion Petra Kvitova also booked her spot in the Wuhan semi-final line-up, easing past 19-year-old Dayana Yastremska of Ukraine 6-2, 6-4 in just 72 minutes.Kvitova, who has been dealing with a forearm injury that forced her out of the French Open this year and is requiring her to wear a sleeve in her matches this week, reached her first semi-final since Stuttgart in April.The 29-year-old Kvitova will face off with Alison Riske on Friday after the American upset third-seeded Elina Svitolina 6-1, 6-3 to record the third top-five victory of the year.Riske had never beaten Svitolina before and knew she was in for a gruelling affair. The first game alone lasted 14 minutes, before Riske managed to take control of the match.”I knew it was going to be a battle. I think mentally I was just prepared for that,” said the world number 35. “I’m just really pleased with the way I competed.”Riske will be contesting her sixth career semi-final at a Chinese event. Ashleigh BartyatpStefanos Tsitsipastennis First Published: September 26, 2019, 10:16 PM IST Get the best of News18 delivered to your inbox – subscribe to News18 Daybreak. Follow News18.com on Twitter, Instagram, Facebook, Telegram, TikTok and on YouTube, and stay in the know with what’s happening in the world around you – in real time.