Dinara Safina suffered a shock defeat at the hands of wild card Shuai Zhang in the second round of the China Open.

Safina is set to lose her world number one ranking as a result of her loss to Shuai.

The Russian has held the top spot since April despite failing to win a grand slam title, provoking fierce criticism of the rankings system.

Serena Williams, who has won two of the four major titles this season while remaining behind Safina, has made her feelings known but she is now set to overtake her rival if she wins her second-round match against Ekaterina Makarova tomorrow.

Top seed Safina had her chances against Shuai, ranked a lowly 226 in the world, particularly in the second set, where she was a break ahead and squandered a set point before going down 7-5 7-6 (7/5).

Third seed Venus Williams was beaten by Russian teenager Anastasia Pavlyuchenkova for the second successive tournament as she crashed out in the second round.

After losing in the first round to the 18-year-old in Tokyo last week, Williams continued her disappointing recent form with a 3-6 6-1 6-4 defeat at the Beijing Olympic Green Tennis Center today.

Sixth seed Svetlana Kuznetsova had no such problems as she cruised into the third round with a 6-2 6-1 victory over Anabel Medina Garrigues while Aleksandra Wozniak and Alona Bondarenko also made progress.

In first-round action, 13th seed Nadia Petrova battled past qualifier Alla Kudryavtseva 6-1 5-7 6-2 while Daniela Hantuchova saw off Spain's Carla Suarez Navarro 7-5 6-2.

Francesca Schiavone had won the first seven games against Sabine Lisicki when the German retired with illness. Alisa Kleybanova and Vania King also reached the second round.

In the men's event, second seed Novak Djokovic safely negotiated his first-round test, beating Romania's Victor Hanescu 6-3 7-5.

The Serbian is making his debut at the China Open but won the bronze medal at last summer's Olympics at the same venue.

Philipp Kohlschreiber saw off the challenge of Ivo Karlovic despite the giant Croatian taking his tally of aces for the season to 800.

The German eventually prevailed 7-6 (8/6) 4-6 6-1 to join Julien Benneteau and Tommy Robredo in the second round.

Eighth seed Marin Cilic, a quarter-finalist at the US Open, defeated Russia's Igor Andreev 6-4 6-4 in their first-round match while Juan Carlos Ferrero edged past Nicolas Almagro 7-5 7-6 (7/3).

In the final women's match of the day, home star Na Li recovered from a break down in the final set to beat Lucie Safarova 4-6 6-0 6-4 and reach the third round.