China's Li Na sends down a return during her singles match against Belarus's Olga Govortsova yesterday at the Australian Open.
Zheng showed grit as she foug ht back from a losing position in the final set on Rod Laver Arena, reeling off five games in a row against the panicking ninth seed to take it 6-4, 1-6, 7-5.
Afterwards Zheng, who reached the semifinals in 2010 and is a two-time grand slam doubles champion, revealed that tenacity had been drummed into her from a young age.
"I know I'm not tall, I'm not strong. My coaches told me, if you want to go far, you need to keep fighting for every ball and focus for every point," she said. "So, yeah, this is my game."
Zheng was never going to be a pushover - she beat Stosur in Sydney last week.
Stosur admitted her problem was mental, not physical. "Oh, I think it's 100 percent (mental)," she said. "I think that's what it was. I got tight and then you start missing some balls. You probably think a little bit too much."
Li, the 2011 French Open champion and Australian Open runner-up, also faced difficult moments in her 6-2, 7-5 win against Olga Govortsova of Belarus before booking her place in the next round.
"She started the second set much better so I'm just happy to win," said Li, adding that she was confident of adding to her solitary grand slam title in 2011. "Australia for me - I really believe I can win this grand slam."
With Peng Shuai's win on Tuesday, three Chinese women are into the third round in Melbourne, in positive signs for the country which will host five WTA tournaments next year.
Chinese Taipei qualifier Chan Yung-jan went out to former women's world No. 1 Ana Ivanovic, failing in her bid to join compatriot Hsieh Su-wei in the round of 32.
Japanese star Kei Nishikori, a men's quarterfinalist last year, also made it to round three as he came through a first set tie-break and then surged home in straight sets against Argentina's Carlos Berlocq.
"It's the Asian Grand Slam, and like you see today, I had a lot of support, and that makes me play better.
"Yeah, I love it."