The Chinese player advanced from the second stage of the tournament after beating the American over three sets at Flushing Meadows.
Having knocked off the former world number one, Zheng feels that her win will help her going into the rest of the tournament.
"Today is tough match for me. Unbelievable I can beat her," Zheng told reporters. "The second set I lost my concentration and she played so great.
"The final set we were fighting each other. I think this is very good for me and will help me for the next match."
Zheng will face Carla Suarez Navarro in the next round.