Jelena Jankovic of Serbia reacts to a missed point against Elena Dementieva of Russia during their semi-final match at the US Open tennis tournament at Flushing Meadows in New York, September 5.- Xinhua/Reuters

Top seed Jelena Jankovic blazed into the quarterfinals of the Pan Pacific Open in Tokyo with a crushing 6-2, 6-1 victory over Italian Flavia Pennetta yesterday.

But fellow Serb Ana Ivanovic suffered a shock exit when the French Open champion was upset 6-1, 1-6, 6-2 by Russian Nadia Petrova in her opening match on the shore of Tokyo Bay.

Jankovic, beaten by Serena Williams in the US Open final earlier this month, will recapture the world No. 1 ranking from the American if she wins in Japan.

She overpowered Pennetta in a match played under a closed roof because of an approaching typhoon, wrapping up an easy win with an ace after just 61 minutes.

"I would like to be No. 1 again," Jankovic told reporters. "But the most important thing is to finish the year as the No. 1 player."

Jankovic faces Russian Svetlana Kuznetsova next after the fifth seed blew away Japan's Ayumi Morita 6-1, 6-1.

Second seed Ivanovic, who had declared herself fully fit after withdrawing from last month's Beijing Olympics with a thumb injury, lost after an error-strewn performance.

"I haven't played many matches so I'm happy to get back playing again," she said. "It was obviously frustrating but the surface was very fast and she was going for her shots."

Earlier, Olympic champion Elena Dementieva booked her place in the season-ending WTA Championships by crushing France's Alize Cornet 6-0, 6-3 in her opening match.

The world No. 4, who won gold in Beijing last month, took just 69 minutes to reach the last eight of the US$1.34 million Pan Pacific tournament.

Dementieva, the Pan Pacific Open's third seed, became the fifth player to qualify for November's showcase event in Doha, exclusive to the world's top eight.

"It's great to be there months before," said the Russian, winner in Tokyo two years ago. "I remember years before fighting right up to the end to get into the tournament."

Williams, Jankovic, Ivanovic and Russian Dinara Safina have already secured their spots in the US$4.45 million end-of-season shootout.

Six of the world's top 10 players are appearing in Tokyo, although No. 1 Williams is not taking part.

In China, top-seeded Vera Zvonareva of Russia beat China's Xu Yifan 6-1, 7-6 (4) yesterday to move into the quarterfinals of the Guangzhou International.

Zvonareva, a bronze medalist at last month's Olympics, will next face Italy's Karin Knapp, who beat eighth-seeded Mariya Koryttseva of Ukraine on Wednesday.

Austria's Tamira Paszek defeated seventh-seeded Pauline Parmentier of France 6-2, 2-6, 6-3. Her next opponent will be unseeded American veteran Jill Craybas, who on Wednesday upset sixth-seeded Olga Govortsova of Belarus.