Wozniacki is looking for back-to-back titles after winning in Tokyo
Top seed Caroline Wozniacki beat Italy's Sara Errani 6-4 6-2 in her opening match at the China Open to close in on the world number one spot.
The 20-year-old Dane will overtake Serena Williams at the top of the rankings if she beats Petra Kvitova in the quarter-finals.
Second seed Vera Zvonareva made the last eight with a 5-7 6-4 6-2 win over fellow Russian Maria Kirilenko.
In the men's event, Novak Djokovic had a walkover when Mardy Fish pulled out.
The defending champion and top seed enjoyed the easiest of passages into the last eight when American Fish withdrew with an ankle injury just hours before the match.
Fourth seed Nikolay Davydenko battled past Marin Cilic 7-5 7-5 and will next face John Isner, who defeated Philipp Kohlschreiber 7-6 (7-3) 3-6 6-3, while Gilles Simon also progressed.
Wozniacki won a WTA Tour-leading fifth title of the year in Tokyo last week and if she reaches the quarters in Beijing she will become number one in the world on 11 October.
"To be honest, I don't think about it," insisted the Dane. "I'm really happy to be here and that I won my match today. Tomorrow is just another match, and hopefully I can win it and pull through. We'll have to see."
Alreayd through to the last eight, along with Zvonareva, are fifth seed Francesca Schiavone, 15th seed Shahar Peer of Israel and Switzerland's Timea Bacsinszky.