BEIJING (AP) -- Two-time champion Novak Djokovic reached the China Open quarterfinals after dismissing Carlos Berlocq of Argentina 6-1, 6-3 on Wednesday.
Djokovic rushed through the first set then lost his serve twice in the second before winning the second-round match.
The Serb, champion in 2009 and 2010 in his only previous appearances in Beijing, faces Jurgen Melzer on Friday after the Austrian defeated Alexandr Dolgopolov 7-6 (9), 2-6, 6-1.
Florian Mayer of Germany also made the last eight.
Women's defending champion Agnieszka Radwanska needed more than two hours to put away Spanish qualifier Lourdes Dominguez Lino of Spain 2-6, 6-1, 6-4.
Radwanska, coming off a loss in the final of the Japan Open on Sunday, struggled in her first matchup against the Spaniard. Radwanska broke six times and lost her own serve seven times.
Second-ranked Maria Sharapova downed Sorana Cirstea of Romania 6-2, 6-2, and Slovenian qualifier Polana Hercog rallied from 5-1 down in the third set to beat Ekaterina Makarova 7-6 (5), 3-6, 7-6 (3).
Ana Ivanovic and Jelena Jankovic were knocked out of the third round in straight sets.
Ivanovic was ousted 6-4, 6-3 by Romina Oprandi of Switzerland, who replaced an ill Serena Williams in the draw.
Jankovic fell apart after leading 5-2, going out to Carla Suarez Navarro of Spain 7-5, 6-4.
"Jelena is always difficult to play, but I played well," Suarez Navarro said. "She always fights a lot, and I'm happy to have finished it off."