The women's draw, which has already seen top seed Agnieszka Radwanska and former world number one Caroline Wozniacki sent packing, lost the third-seeded Italian, last year's surprise French Open semi-finalist, in what was a surprise loss to Bulgaria's Pironkova.
The Italian world number seven took a medical time-out in the second set to have treatment on her lower back, raising concerns over her fitness ahead of the year's first grand slam.
Sam Stosur's stuttering revival after a dismal Hopman Cup continued with a second straight win at the Hobart International in front of home fans.
The former U.S. Open champion had to save two match points against 54th-ranked Frenchwoman Kristina Mladenovic as she laboured through a 6-4 2-6 7-6 (9-7) match blighted by an astonishing 22 double-faults from both players.
- Sports & Recreation
- Agnieszka Radwanska
- Caroline Wozniacki