Fifth seed .
Markarova became the fifth seeded player to suffer an opening-round defeat following the exits of Agnieszka Radwanska, Zhang Shuai, Sorana Cirstea and Aryna Sabalenka.
After losing the first set, Serbia's Krunic powered past her opponent to claim the second in 24 minutes.
Krunic converted an early break in the decider and held on to the advantage with solid defensive play to clinch victory.
Second seed Svetlana Kuznetsova recovered from a mid-match blip against Bulgarian qualifier Viktoriya Tomova to win 7-5 4-6 6-1 in the second round.
Tomova, ranked 165th in the world, grabbed an early break in the decider before her Russian opponent won five consecutive games and closed out the match in just over two-and-a-half hours.
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