Jabeur, No. 204 in the world rankings, is in the draw as a wild-card entrant. It is the 18-year-old's second WTA tournament of the year, the first ending in a first-round loss.
But Wednesday Jabeur gained place in the Baku Cup quarterfinals with a 6-2, 7-5 win over Jovanovski. Jabeur won more than half (40-of-74) of the points off Jovanovski's serve and had three breaks in each set to secure the upset win.
No. 2-seeded Donna Vekic earned her place in the quarterfinals with a 6-1, 6-2 rout of Tetyana Arefyeva. She had five breaks in seven games receiving serve.
No. 4-seeded Alexandra Cadantu also advanced out of the second round, beating Mandy Minella 5-7, 6-1, 6-3. She lost her serve three times in the first set but only once in reach of the last two sets.
The first round was completed Wednesday with Galina Voskoboeva edging sixth-seeded Polona Hercog 7-6 (9-7), 4-6, 6-3 in nearly 3 hours. Voskoboeva won about two-thirds of the points on serve and suffered just two breaks in the match. She lost only seven points on serve in the third set.
No. 3-seeded Chanelle Scheepers topped Andrea Hlavackova 3-6, 6-3, 6-4 while seventh-seeded Elina Svitolina beat Aleksandra Krunic 6-3, 4-6, 6-2 and Kateryna Kozlova defeated Eleni Daniilidou 6-2, 3-6, 6-4 in the other first-round matches Wednesday.