Nadal, who will regain his place at the top of the world rankings if he reaches the final in Beijing, took one hour and 54 minutes to beat Germany's world number 25, 6-4 7-6 (7/3).
Nadal will next face Italy's Fabio Fognini, who beat wild card Lleyton Hewitt 6-0 6-2.
The Spaniard will overtake current world number one Novak Djokovic even if the Serbian beats him in the final.
Eighth seed John Isner beat Spanish qualifier Roberto Bautista Agut 6-2 6-7 (3/7) 6-4 to move into a last-eight meeting with fourth seed Tomas Berdych.
Home favourite Li Na progressed into the women's quarter-finals with a 7-5 6-4 win over Wimbledon finalist Sabine Lisicki.
Li will face ninth seed Petra Kvitova in the last eight after the powerful Czech edged out Italian fifth seed Sara Errani 6-4 6-7 (3/7) 6-3.
In women's second-round action, third seed Agnieszka Radwanska eased past Marion Keys of the United States 6-3 6-2, and eighth seed Jelena Jankovic was a 6-3 5-7 6-3 winner over Galina Voskoboeva of Kazakhstan.
Serbia's Ana Ivanovic went down 1-6 6-4 6-4 to qualifier Polona Hercog, while Germany's Andrea Petkovic also needed to come from behind on her way to beating veteran Russian Svetlana Kuznetsova 4-6 6-4 6-1.