Zhang ousted fifth-seeded Richard Gasquet 6-4, 3-6, 6-4. Zhang had just three break chances in the match but made the most of all of them. The first decided the first set while two in the third allowed him to advance.
Mikhail Youzhny had four breaks in a 6-3, 6-3 win over Kevin Anderson. Youzhny won nearly half (24-of-49) of the points when receiving serve.
Feliciano Lopez topped Lu Yen-Hsun 6-3, 7-6 (9-7) behind 10 aces and winning nearly 70 percent of the points on serve.
Sam Querrey defeated Andreas Seppi 6-1, 6-4 in the final second-round match. Querrey dropped just 12 points over nine service games and didn't face a break point.
Friday's quarterfinal pairing have top-seeded Novak Djokovic playing Jurgen Melzer while Zhang takes on Florian Mayer in the top half of the draw. Lopez meets Querrey and Youzhny goes against third-seed Jo-Wilfried Tsonga in the other matches.