BEIJING -- Second-ranked Aryna Sabalenka was bundled out in the third round of the China Open in straight sets by Nikola Bartunkova on Sunday, while Novak Djokovic maintained his perfect record at the tournament with a 4-6, 6-4, 6-4 victory over US Open champion Alexander Zverev in the quarterfinals.
The No. 34-ranked Bartunkova defeated the four-time Grand Slam champion 6-4, 6-3 in just over an hour and a half to leave the WTA-1000 event without its two top seeds in the first week. Newly crowned world No. 1 Elena Rybakina was ousted Saturday.
Sabalenka, who was denied a three-peat at the US Open last month by Rybakina, squandered five break points in the first set as her historic struggles in Beijing continued. The 28-year-old Belarusian has never progressed past the quarterfinals at the event.
"First of all, I focused on myself, to be calm," Bartunkova said. "And Aryna, she's great, she's a legend, she's a Grand Slam champion. So yeah, I'm really happy that I won the match. ... I'm not a girl who celebrates too much."
Bartunkova will next play 24-year-old Sinja Kraus of Austria, who earlier defeated Dayana Yastremska 6-1, 6-4.
Fifth-ranked Mirra Andreeva eased into the fourth round with a 6-4, 6-1 victory over Polina Kudermetova. This year's French Open winner fired six aces and took five of her seven break-point opportunities to overwhelm her Uzbek opponent in just 68 minutes.
Djokovic is bidding to win his seventh China Open title and is now 32-0 in Beijing, eclipsing Rafael Nadal's 31-0 start at the French Open for the best start at a tour-level tournament in the Open era.
The Serbian player started slowly, dropping his serve in the opening game of the match and eventually losing the first set before bouncing back to take the next two.
"I gave him an early break, and then it was hard to come back in the first set," Djokovic said. "I had a couple of break points when he was serving for the set at 5-4 but didn't use them, but I kind of felt already from midway through the first set that I was starting to get a good rhythm."
Djokovic will next face Daniil Medvedev in the semifinals.
Earlier, Hubert Hurkacz beat Karen Khachanov 7-6 (2), 6-2 and will face Alex de Minaur, who beat Andrey Rublev 1-6, 6-2, 6-3, in the other semifinal.