(Photo credit: Geoff Burke)

Czech No. 26 seed Nikola Bartunkova sent No. 2 seed Aryna Sabalenka of Belarus to an early exit from the China Open, beating the four-time Grand Slam winner 6-4, 6-3 on Sunday in Beijing.

One day after World No. 1 Elena Rybakina of Kazakhstan was knocked out of the WTA 1000 event in the Round of 64, Sabalenka had to pack her bags after a Round of 32 loss.

'It is the biggest win of my career,' said Bartunkova, 20, who only made her WTA 1000 debut this year. 'It was very difficult conditions for today because half of the court was very cold and very windy. And the other side was very hot and opposite. It was very difficult conditions for both of us. It could be better for sure, especially on my serve. But it was because of the (wind) and it was cold. So, that's why I think my percentage of my serve was at the low.'

Bartunkova won a stellar 24 of 29 first-service points (82.8%) and saved all five break points she faced, while Sabalenka managed to go just 26 of 49 (53.1%) on her first-service points.

'She is very talented, and moves well on court,' Sabalenka said of her opponent after the match. 'She also serves well so you have to convert your chances against her. She can serve really well and to return from shade or sun is tricky. I wasn't good at this today.'

Bartunkova's next opponent will be Austria's Sinja Kraus, who beat Ukraine's Dayana Yastremska 6-4, 6-1.

The fourth and fifth seeds -- Russian Mirra Andreeva and Czech Linda Noskova, who each won their first career Grand Slams this year -- had an easier go of things in the Round of 32.

Andreeva needed 68 minutes to sail past Uzbekistan's Polina Kudermetova 6-4, 6-1. Not to be outdone, Noskova prevailed 6-2, 6-1 over Switzerland's Viktorija Golubic in a mere 55 minutes. Like her peers, Noskova commented on the challenging court conditions.

'It was a lot colder and much more windy' than her first match, Noskova said. 'Once the match started, I had gotten into my rhythm and didn't really notice it.'

No. 12 seed Naomi Osaka is also through to the Round of 16 after outlasting Czech 20th seed Sara Bejlek 7-6 (4), 6-4.

Bejlek out-aced Osaka 5-0 and saved 8 of 11 break points, but Osaka won 46 of 60 first-service points (76.7%). The four-time Slam champ saved four set points in the first set to force the tiebreaker. Bejlek went on to save four match points before Osaka prevailed on the 16th point of the final game.

'I'm really happy with how I played,' Osaka said in her post-match interview. '... She's an incredible player, so it's nice to have pulled out a two-set victory against her.'

Osaka's next task will be to take down Czech seventh seed Karolina Muchova, who was a 4-6, 6-4, 6-2 winner over Russian 29th seed Liudmila Samsonova.

The other winners Sunday were No. 19 seed Ekaterina Alexandrova of Russia, who rallied past countrywoman and No. 11 seed Diana Shnaider 3-6, 6-4, 6-3, and Ukraine's Daria Snigur, who nearly shut out Australia's Taylah Preston 6-1, 6-0 in 47 minutes.

--Field Level Media