Top seed Samantha Stosur of Australia overcame a late scare to beat Kristina Mladenovic 6-4, 2-6, 7-6 (9-7) at the Hobart International on Wednesday.
In the day's opening encounter, qualifier and world No. 114 Estrella Cabeza Candela upset the odds as she knocked out third seed Elena Vesnina.
Stosur got off to a poor start in the WTA International hard court second-round clash, losing her first service game, but recovered to edge the opening set.
However, two drops of serve in the second saw her well beaten, before the third went down to the wire.
Stosur, who also struggled to come through her opener against Madison Brengle, found herself 5-2 down at one point in the tie-break, but won two points on her opponent's serve to scrape into the tournament's quarterfinals, where she will meet Serbia's Bojana Jovanovski.
Cabeza Candela lost the opening set 6-4, but made light of the 90-place rankings gap as she stormed to a 6-2 victory in the second.
She maintained that form in the third, before Vesnina was forced to retire with a hip injury with the scores at 4-1.
Cabeza Candela will now meet Monica Niculescu of Romania, who also caused an upset by claiming a 7-6 (7-5), 6-1 triumph over sixth seed Mona Barthel.
Niculescu edged a scrappy opening set, before benefiting from her wasteful opponent's failure to win a single service game in the second.
In the day's remaining encounters, second seed Kirsten Flipkens was pushed all the way by wildcard Storm Sanders in a match that ended 4-6, 7-6 (7-3), 7-6 (7-5), and seventh seed Kara Zakopalova cruised past world No. 51 Zhang Shuai 6-1, 6-2.
Meanwhile, Belgium's Yanina Wickmayer was forced to retire with illness at 4-1 down in the opening set of her match against Spanish qualifier Garbine Muguruza.