Top-ranked Novak Djokovic cruised while Serena Williams was made to fight for her win in the China Open on Tuesday.

Djokovic put away Lukas Rosol of the Czech Republic 6-0, 6-3 in the first round, while Williams lost her serve twice to 2010 French Open champion Francesca Schiavone before prevailing 6-4, 7-5 in the second round.

Djokovic’s run of 100 weeks at the top of the ATP rankings is in danger this week from Rafael Nadal, who defeated Santiago Giraldo of Colombia 6-2, 6-4. Nadal will retake No. 1 if he reaches the final.

Williams found herself having to grind against Schiavone in their second set, losing her serve twice and having to break back each time. Schiavone, who won only one game off Williams at the U.S. Open, won her most against Williams in eight years.

Meanwhile, Venus Williams, a wild-card recipient like Schiavone, fell to Sabine Lisicki of Germany for the first time in four years, 6-1, 6-2. Lisicki didn’t face a break point and broke Venus three times.

Djokovic will take on Fernando Verdasco in the second round after the Spaniard beat Indian qualifier Somdev Devvarman 7-6 (6), 6-3.

Nadal’s second-round opponent will be Philipp Kohlschreiber of Germany.

In other men’s matches. fifth-seeded Richard Gasquet of France beat Florian Mayer of Germany 6-3, 7-6 (2); sixth-seeded Stanislas Wawrinka of Switzerland overcame Andreas Seppi of Italy 4-6, 6-3, 6-4, and eighth-seeded John Isner of United States beat local Di Wu 5-7, 7-6 (4), 6-3 after nearly two hours.

Former No. 1 Caroline Wozniacki beat Monica Niculescu of Romania 6-3, 6-1 to remain on course to face Williams in the quarterfinals.

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