Tomas Berdych and Caroline Wozniacki both lost their way in Beijing's choking smog as they exited the haze-hit China Open with tough defeats on Wednesday.

As air pollution hovered at "hazardous" levels and fans in face masks became commonplace, Berdych was sent packing just 24 hours after arriving from his victory in the rain-delayed Shenzhen Open final.

The Czech world No 5 never hit his stride against Uruguay's 37th-ranked Pablo Cuevas as he was dumped out 6-4, 6-4 to become the roller-coaster tournament's latest upset.

"I made one tournament title. The other one didn't go my way," shrugged Berdych, who won his 11th career title in Shenzhen, southern China, on Monday.

"It's always a difficult part of the year," he said. "We have to travel a lot. The conditions are always very different, very difficult, week by week here in China. It's not easy to adjust."

Later Wozniacki was brutally disposed of by a grimly determined Angelique Kerber 6-2, 6-3 as her hopes of reaching the year-ending WTA Finals took a hit.

Andrea Petkovic was also bundled out by Sara Errani 3-6, 6-3, 6-2, compounding a tough season which has included food poisoning, injury and a first-round defeat last week in Wuhan.

"After Wuhan, I said to my coach, this is the worst season I've ever played. That was my assessment after Wuhan. But I guess I was quite emotional after losing in the first round," she said.

It was a different story for Garbine Muguruza, who retired from last week's Wuhan final against Venus Williams with an ankle problem but bounced back to beat Irina Falconi 6-2, 6-1.

The Spaniard, nicknamed 'Mushroom' by Beijing fans because her name sounds like "mushroom" in Chinese, will now qualify for the WTA Finals if she wins her next match against Mirjana Lucic-Baroni.

"I think I want to finish the year in a good way. I want to go on holidays and say, 'Look, I had a great year, I did everything I could'," she said.

Fourth seed Agnieszka Radwanska set up a quarterfinal with Kerber after Madison Keys retired after their first set, becoming the latest in a long list of casualties.

"Definitely tough," said the Pole, when asked about the air pollution, which soared to a level at which people are advised to avoid outdoor exertion.

"A little bit different than usual. But I think we're all kind of used to it, right? We're coming to Beijing every year. We can expect more or less humidity or the pollution."

Rafael Nadal sparked his China Open campaign into life as he stormed into the quarterfinals with a much-improved 7-6 (3), 6-4 victory over Canada's Vasek Pospisil on Wednesday.

The 14-time Grand Slam winner had his service broken four times in the first round by China's 230th-ranked Wu Di, but he showed better signs against Pospisil, the world No 44.

Spain's Nadal, groping for form after a difficult year, will now face America's Jack Sock in the last eight as he looks for a confidence-boosting fourth title of the season.

"Every improvement is important," said Nadal. "Obviously I improved from yesterday. I played a much better match than yesterday."