BEIJING: Dinara Safina and Serena Williams, the world number one and two, struggled but advanced Sunday to the second round of the China Open as the US superstar looks to wrest the top ranking from the Russian.

Williams, 28, surrendered a few early service breaks but steadied herself with precise play from the backcourt to defeat Estonia's Kaia Kanepi 7-5, 6-4.

The younger of the Williams sisters kept the pressure on Kanepi, eventually forcing the 24-year-old to send a sliced backhand into the net to end the first set.

The pair stayed on serve for most of the second set, but Williams sealed the win when she broke the 48th-ranked Kanepi for the fifth time in the final game.

"It was a good challenging match to start out with. It wasn't easy but I felt like I was hitting a clean ball," Williams said after the match.

"She's a really good player. She always plays me really tough."

Safina, looking to bounce back after an embarrassing loss last week in Japan to a teenage Taiwanese qualifier, defeated Italy's Roberta Vinci 6-4, 6-4, but the match was not as straightforward as the score suggested.

The pair traded breaks throughout the match, with Safina losing her serve four times and the 26-year-old Vinci surrendering hers six times.

"There is still room for improvement in my game," Safina told reporters.

"She's not an easy one to play... you have to really pick the right shot to go for it. She has a great touch."

The 23-year-old Safina will face Chinese wild card Zhang Shuai in the second round, while Williams will take on Russia's Ekaterina Makarova.

Williams only needs to have a better result than Safina in Beijing to claim the number one ranking, according to WTA officials.

While the Russian said she did not think much about the points race, the American has her sights firmly set on the top spot.

"It's definitely on my radar," Williams said. "I would love to be number one but I also want to pay the price to be number one. And it'll come eventually."

In other matches, Svetlana Kuznetsova, the tournament's sixth seed and reigning French Open champion, survived a scare from China's Zheng Jie, falling behind early in both sets but outlasting her opponent 7-6 (7/3), 7-5.

The 24-year-old Russian -- who is ranked sixth in the world and won the China Open in 2006 -- brought herself back into contention with powerful ground strokes and Zheng, the world number 32, did not rise to the occasion.

"I think that I started both sets pretty slow. I wasn?t quite moving well," Kuznetsova said after the match.

"Then when I started to move better, I started to play better. Then I lost my concentration again, and then got it back and started to play better."

Russia's Elena Dementieva, the fourth seed, advanced with a 6-4, 6-0 win over Germany's Anna-Lena Groenefeld, but number five Caroline Wozniacki of Denmark was a surprise loser to Spain's Maria Jose Martinez Sanchez in three sets.

Third seed Venus Williams of the United States advanced to the second round on Saturday.

In other first round matches on Sunday, Russian seventh seed Vera Zvonareva beat Romania's Sorana Cirstea 6-2, 6-2, and Switzerland's Patty Schnyder got past Poland's Urszula Radwanska 6-4, 7-5.

Ninth seed Victoria Azarenka of Belarus advanced, easily defeating compatriot Olga Govortsova 6-1, 6-3.

The men's main draw gets under way on Monday, with Rafael Nadal, Novak Djokovic and Andy Roddick leading the charge.