Stosur, US Open champion in 2011, was serving for the match before her nerves seemed to get the better of her, allowing Zheng to claw her way back and reel off five successive games to clinch a place in the third round against Julia Goerges.
The 28-year-old Stosur had minor ankle surgery late last year and lost in the opening round of both the Brisbane and Sydney tournaments before the start of the Australian Open.
Stosur, who lost to Zheng in the first round at Sydney last week, handed victory to her Chinese opponent when she double faulted on match point. Stosur has never advanced past the fourth round at Melbourne Park.
(Reporting by Greg Stutchbury; Editing by Peter Rutherford)