Zheng posted three of her seven breaks on the day in the third set in ousting the fourth-seeded Zhang 7-6 (7-4), 2-6, 6-2 in a match that took more than 3 hours. Zheng also had her serve broken seven times but only once in the decisive third set.
Both players suffered through four-break first sets with Zheng taking the tiebreaker. Zheng didn't manage a break opportunity in the second set but cashed in all three of her chances in the final set.
That proved to be the only upset of the day as the top three seeds advanced to Friday's semifinals.
No. 1-seeded Timea Babos, yet to drop a set this week, defeated seventh-seeded Tamarine Tanasugarn 6-3, 6-3 behind five breaks in nine receiving games.
Misaki Doi, the second seed, took out Eri Hozumi 6-4, 6-3 despite nine double faults and four lost service games.
Third-seeded Shahar Peer got by No. 6-seeded Zhou Yi-Miao 6-4, 3-6, 6-3 with four third-set breaks.