Top seed and defending champion Bojana Jovanovski crashed out of the Baku Cup after being beaten 6-2 7-5 by Ons Jabeur in the second round.
Tunisian wildcard Jabeur, who is ranked 204th in the world, came through to win in an hour and 24 minutes to hand her Serbian opponent a shocking defeat.
There were no such problems for fourth seed Alexandra Cadantu, although she was pushed all the way in a match which lasted two hours against Mandy Minella. Romania's Cadantu dropped the first set before winning 5-7 6-1 6-3.
Second seed Donna Vekic booked her place in the next round with a straightforward 6-1 6-2 win over Tetyana Arefyeva while third seed Chanelle Scheepers defeated Andrea Hlavackova 3-6 6-3 6-4.
Elsewhere in the Azerbaijani tournament, Galina Voskoboeva, Elina Svitolina and Kateryna Kozlova all came through their first-round matches.