Kvitova proves too hot even for in-form Wozniacki in Beijing
Victorious Nadal wary of Isner at China Open and Raonic pulls out of Japan Open
Rafael Nadal said he was braced for the "huge" serve of John Isner after Spain's world No 1 bulldozed his way into the China Open quarter-finals on Thursday.
The 16-time grand slam champion Nadal saw off the young Russian Karen Khachanov 6-3, 6-3 to set up a clash with Isner in Beijing.
The in-form American, the sixth seed, is renowned for his booming service game and Nadal expects to come under a barrage on Friday.
Isner was impressive in blasting his way past Argentina's Leonardo Mayer 6-0, 6-3.
"Tomorrow will be a tough one against Isner, he's playing unbelievably well," Nadal said. "I saw him today, he played so aggressive, having a lot of success, hitting a lot of winners, returning very well.
"Everybody knows that he serves huge and it is so difficult to break him.
"But if you add that he is playing very well now from the baseline, he is one of the toughest opponents you can meet."
Nadal, 31, the top seed and coming off the back of a third US Open title, saved two match points against Frenchman Lucas Pouille in his opener in Beijing.
But he was always in control on Beijing's outside hard courts against Khachanov, 21, breaking him in the fourth game of the first set on the way to a routine victory.
Andrey Rublev ensured a continued Russian presence in the men's draw as he sprang a surprise in fighting back to oust seventh seed Tomas Berdych 1-6, 6-4, 6-1.
Kvitova overcomes Wozniacki
In the women's draw, a heavyweight clash pitched two-time Wimbledon champion Petra Kvitova against Denmark's former No 1 Caroline Wozniacki.
The Czech Kvitova, seeded 12, stormed through the first set 6-1 and although Wozniacki was better in the second set, Kvitova broke her for 6-4 and will play compatriot Barbora Strycova in the quarters.
Another former world No 1, fourth seed Karolina Pliskova, became another high-profile casualty, going out to unseeded Sorana Cirstea.
Cirstea follows fellow Romanian Simona Halep into the quarter-finals after the second seed sent Maria Sharapova packing on Wednesday.
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Cirstea, ranked 44 in the world, stunned the Czech Pliskova 6-1, 7-5 to reach the last eight.
She will play Latvia's Jelena Ostapenko, the Roland Garros champion, after China's top player Peng Shuai retired with a knee injury at 3-0 down in the first set.
Peng, 31, said she had been having injections to ease the pain and her right knee was heavily strapped, but she could not play on.
"The doctor suggested I should take a period of rest and get it treated, but I can only rest after the season, that's the plan," said Peng, ranked 25 in the world.
World No 1 Garbine Muguruza and reigning champion Agnieszka Radwanska are both out, leaving world number two Halep as the favourite in the Chinese capital.
Also into the quarters is Caroline Garcia, who defeated French compatriot Alize Cornet 6-2, 6-1 and will play third seed Elina Svitolina of Ukraine.
Garcia is in red-hot form after winning the Wuhan Open on Saturday.
More injury woes to Raonic
Canadian Milos Raonic's injury woes continued on Thursday as he was forced to retire from his second-round match against local favourite Yuichi Sugita at the Japan Open.
The former world No 3, playing his first tournament since undergoing wrist surgery, lasted just eight minutes of his clash with Sugita.
Raonic had looked sharp in battering battered Serbian Viktor Troicki 6-3, 6-4 on Tuesday.
But the third seed was forced to call for the trainer during the first game, clutching his right calf.
He eventually threw in the towel, wincing with discomfort and limping despondently off court.
Raonic's misfortune is Marin Cilic's gain, as the Canadian's retirement opens up the draw for the big-serving Croatian, with no seed left in his half.
The highest-ranked player in the bottom half of the draw is Belgium's David Goffin, who ended a wretched run of six defeats in his previous six finals by capturing the Shenzhen Open this month.
Goffin, instrumental in Belgium's run to next month's Davis Cup final, had a scare against Australian qualifier Matthew Ebden, losing the first set before coming through 2-6, 7-5, 7-6.
The Belgian will meet Frenchman Richard Gasquet in the quarter-final after he eased through his encounter with Taipei's Lu Yen-hsun 6-0, 7-6.
Gasquet inflicted the dreaded "bagel" in the first set against his 63rd-ranked opponent.
The second set was much tighter but Gasquet -- who has slipped from seventh to 30th in the world - clinched the tie-break 7-5 to book his place in the last eight after one hour and 28 minutes.
The 31-year-old has struggled with injuries but a recent return to the second-tier Challenger circuit appears to have boosted his confidence.
Gasquet won last month in Szczecin and he hopes to repeat his 2007 performance in Tokyo, where he reached the final.
Meanwhile, American Steve Johnson followed up his surprise win over Austrian wunderkind Dominic Thiem with a 6-2, 6-4 victory over Ukraine's Aleksandr Dolgopolov.
Johnson was especially dominant on first serve, winning an impressive 93 per cent of points and 100 per cent in the first set.
He next faces eighth seed Diego Schwartzman after the Argentine disposed of Australia's Bernard Tomic.
Cilic heads the Tokyo field this year at a tournament whose list of former champions includes tennis greats Ken Rosewall, John McEnroe, Pete Sampras, Roger Federer and Rafael Nadal.