Andrea Petkovic suffered a surprise defeat in the first round of the Istanbul Cup as world number 420 Dayana Yastremska fought back from a set down to earn her maiden WTA Tour win.

Eighth seed Petkovic, ranked 342 places above her 16-year-old opponent, looked on course for a routine success as she took the first set.

But wildcard Yastremska hit back in remarkable fashion by bagelling the German before recovering from a break down in the decider to see out a 3-6 6-0 6-3 triumph.

In Monday's other match, Maria Sakkari defeated Danka Kovinic 7-6 (7-3) 6-3.