Jankovic and Kuznetsova battle through

NEW YORK (Reuters) - Second seed Jelena Jankovic and former champion Svetlana Kuznetsova had to work much harder than expected to shake off their opponents in the second round of the U.S. Open on Wednesday.

Serb Jankovic squandered a match point in the second set before scraping past Swede Sofia Arvidsson 6-3 6-7 7-5 and Russian Kuznetsova overcame a slow start to beat Romanian teenager Sorana Cirstea 7-6 6-1.

Olympic champion Elena Dementieva, however, had no complaints about not playing to her potential after completing a 6-2 6-1 demolition of Pauline Parmentier of France.

Jankovic, who reached the last four at the U.S. Open in 2006, needed two hours and 45 minutes to subdue the 63rd-ranked Arvidsson on the Arthur Ashe Stadium court.

The 23-year-old Serb twice served for the match in the second set and also led 3-0 in the tiebreak before the Swede pegged her back with a series of stinging groundstrokes.

Jankovic, who briefly claimed top spot in the rankings earlier this month, had to hold off another Arvidsson comeback in the decider before booking her place in the third round.

"It was a really tough one and I am completely out of breath," said a relieved Jankovic who will next face Wimbledon semi-finalist Zheng Jie. "I struggled out there and my opponent played really, really well and pushed me to the limit.

"I am not yet at my full potential. I still have a long way to go to be where I want to be."

Kuznetsova, who clinched the 2004 title in an all-Russian final with Dementieva, trailed world number 53 Cirstea 4-2 in the opening set before raising the level of her own game.

"Today I played much better than my first match, so it's looking good for me," the third seed said after setting up a meeting with 28th-seeded Slovenian Katarina Srebotnik.

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"Definitely I'm not in my best shape now and I haven't been playing well before the U.S. Open. But grand slams keep me much more motivated and I do much more better in grand slams."

Eighth-seeded Vera Zvonareva became the latest casualty at Flushing Meadows, losing 6-3 6-3 to Tatiana Perebiynis of Ukraine, while 1998 champion Lindsay Davenport needed to rely on her greater wealth of experience to steer past Russian teenager Alisa Kleybanova 7-5 6-3.

Serbian third seed Novak Djokovic, beaten in last year's final by Roger Federer, survived an injury scare before beating Frenchman Arnaud Clement 6-3 6-3 6-4 in the first round of the men's event.

The Australian Open champion appeared to turn his left ankle midway through the third set but recovered to wrap up victory in just under two hours.

"It's okay," Djokovic said of his foot. "It's going to be good in two days, I'm sure. I was thinking more of it than I was actually feeling the pain, so it's not really a big deal.

"In that certain moment, I felt big pain so I just had to tape the ankle. But it's going to be all right."

Fifth-seeded Russian Nikolay Davydenko made even smoother progress, charging into the second round with a comfortable 6-3 6-3 6-3 win over Israel's Dudi Sela.

The Russian has not won back-to-back matches since winning a low-key claycourt tournament in Warsaw in June but appeared to have regained his form to dispatch Sela.

In the final match of the night session, big-serving local favorite Andy Roddick, the 2003 champion, powered down 15 aces to ease past Frenchman Fabrice Santoro 6-2 6-2 6-2.

"I was really excited about the way I was playing and glad with the way I served because I haven't been serving that well," the eighth-seeded American said. "If I can do that, I like my chances of holding which puts pressure on the other guy."

(Editing by Larry Fine)