Zhang's 6-4, 6-2 victory over Magdalena Frech was her fourth win in Beijing and all in straight sets - having come into the event after losing 24 singles matches in a row.
The barren run lasting more than 600 days was the second-longest on the WTA Tour in the Open Era, which began in 1968.
Zhang, a former two-time Grand Slam quarter-finalist who has been plagued by injury, again made a nonsense of her ranking against the world number 31 Frech from Poland.
Zhang, a former top-25 player who has won two major doubles titles, will face Spain's 19th-ranked Paula Badosa in the last eight.
The lowest-ranked player to ever reach this stage of the China Open, Zhang raced away with the second set against Frech in front of a packed Beijing crowd on her country's national day.
She had two match points when serving at 5-1. Frech just about held on, but it was only a temporary reprieve.
Zhang struck a defiant pose immediately afterwards, standing still with her arms crossed and beaming.
