The sixth-seeded Stosur lost to 80th-ranked qualifier Kaia Kanepi of Estonia 6-4, 6-4 on Tuesday, the Australian's fourth first-round exit in eight appearances at the All England Club.
Stosur entered Wimbledon with a tour-leading 35 match wins in 2010 and with her career-best ranking. She reached her first Grand Slam final at the French Open this month, beating current No. 1 Serena Williams and former No. 1s Justine Henin and Jelena Jankovic along the way.
The woman Stosur lost to in the final at Roland Garros, Francesca Schiavone, lost her opening match at Wimbledon on Monday.