In fierce heat, Serbian Jankovic lost Akgul Amanmuradova 7-6, 6-4, and the Uzbeki qualifier now goes on to face another Serb, Ana Ivanovic.
A lesser shock, but a surprise nonetheless, was Dane Wozniacki falling to France's Marion Bartoli 6-4, 6-1.
Completing a trio of upsets, Russian sixth-seed Vera Zvonareva went out in straight sets, 6-4, 6-3 to Italian Flavia Pennetta.
Dane Wozniacki was 4-3 up in the first set but then Bartoli rallied to claim the opening frame and then dominated the second where she won 14 of 16 first-serve points.
Wozniacki flew out to Ohio after winning the Danish Open last week and said she may have paid the price for that schedule.
"Definitely it was a factor, there is no doubt about that, getting here late and then getting used to the weather and playing outdoors," she said.
"But it was my choice to play there and then come here," she added.
Bartoli will play the winner of the match between Russian Maria Sharapova and Pole Agnieszka Radwanska.
Eighth-seeded Na Li of China also suffered a premature departure, losing to Belgian Yanina Wickmayer 2-6, 6-2, 7-6 in an exciting three-set encounter.
Ivanovic again looked in good form as she confidently defeated Russia's Elena Vesnina 6-0, 6-3.