)
The Serbian top seed slumped to a 6-2 7-5 loss to Ana Bogdan on the hard courts in Brazil on Tuesday.
Jankovic simply missed her chances as her poor year continued, converting just five of 18 break points.
Every other seed in action managed to reach the quarter-finals.
Irina-Camelia Begu thrashed Paula Cristina Goncalves 6-1 6-2 to set up a meeting with Nao Hibino, who overcame Veronica Cepede Royg 6-3 7-6 (8-6).
)
)
)
Monica Puig crushed Olga Savchuk 6-0 6-4 and next faces Naomi Osaka, who also had a comprehensive win by beating Montserrat Gonzalez 6-3 6-0.
Timea Babos cruised past Alize Lim 6-0 6-1, Jelena Ostapenko beat Catalina Pella 6-2 6-3 and Bogdan's next opponent Lyudmyla Kichenok battled past Tereza Martincova 1-6 6-4 7-6 (7-1).