TOKYO - Former French Open champion Li Na shrugged off a nasty cough to beat Russia's Anastasia Pavlyuchenkova 7-5 4-6 6-2 and reach the last 16 of the Pan Pacific Open on Tuesday.

One of three Chinese players who made the trip to Tokyo despite a blazing political row between her country and Japan, Li's experience told after a wobble in the second set.

"Obviously I'm still not 100 percent," Li told Reuters. "Just trying to stay healthy and taking (cough) medicine every morning and every night."        

However, 2011 Wimbledon champion Petra Kvitova was bundled out in the first upset of the $2.16 million tournament, suffering a 6-4 6-4 defeat by Croatia's Petra Martic.

Li's appearance in Tokyo was a relief for organisers after China withdrew its badminton players from the Japan Open earlier this month amid escalating tensions over Diaoyu Islands in the East China Sea.

Playing on an outside court, last year's Roland Garros winner lacked sharpness after a whirlwind book-signing tour in China following the release of her autobiography.

But the 30-year-old Li saved her best for the big points, putting the match away by smashing a cross-court backhand into the corner after two hours, 37 minutes.

"I practiced on every court because you never know where they are going to put you," said Li. "It was very windy in the morning but I felt fine."  

Fourth seed Kvitova frittered away several opportunities against her 72nd-ranked opponent, who closed out the match with a fierce serve which almost knocked the Czech over.

"That was the biggest win of my career so far," Martic told Reuters. "The last five or six days have been really weird. I've played bad in practice and just couldn't do anything.

"I just decided to enjoy the tournament and see what happens, not put any pressure on myself," added the 21-year-old, who reached the fourth found of this year's French Open.

"I played great today. I played at a very high level so I hope that continues."

Martic next faces Russia's Nadia Petrova after the 17th seed beat Romania's Simona Halep 7-6 6-0.

World number one Victoria Azarenka and twice Pan Pacific champion Maria Sharapova were among the top-ranked players also playing later on Tuesday.

Nine of the world's top 10 women are appearing in the WTA premier five event, US Open champion Serena Williams the only player absent.

Germany's Angelique Kerber made short work of Japanese wildcard Ayumi Morita, the fifth seed comfortably winning 6-3 6-4 to reach the third round.

Sixth seed Sara Errani of Italy beat Sweden's Johanna Larsson 6-3 7-6 and next faces Frenchwoman Marion Bartoli after the ninth seed's 6-2 7-5 win over German Julia Goerges.