Ajla Tomljanovic has produced the shock of the day at the WTA’s St. Petersburg Ladies’ Trophy with a hard-fought win over fifth-seeded Marketa Vondrousova.

World No.57 Tomljanovic came back from a set down on Tuesday to prevail 3-6 6-3 6-4.

The Australian will next face Russian teenager Anastasia Potapova, ranked 44 spots below Tomljanovic, with the winner advancing to the quarter-finals.

Last year’s runner-up Donna Vekic moved into the second round with a straight-sets victory over qualifier Kristie Ahn.

Croatian seventh seed Vekic had too much experience for the American qualifier and sealed a comfortable 6-4 6-1 win in just over an hour.

Vekic will next play Russian No.1 Ekaterina Alexandrova, who saw off compatriot Daria Kasatkina 6-4 3-6 6-4.

Belgium’s Alison Van Uytvanck beat former tournament winner Kristina Mladenovic of France 6-4 6-1 and will go on to face third-seeded Petra Kvitova, the 2018 champion, in round two.

Veteran former world No.2 Svetlana Kuznetsova beat American Jennifer Brady 6-3 6-1 to set up a match with Swiss top seed Belinda Bencic.