Second-seeded Sloane Stephens defeated Andrea Petkovic of Germany 7-6 (1), 4-6, 6-3 at the Generali Ladies to reach her seventh quarterfinal of the season on Thursday.
The 12th-ranked American won just two of the first 14 points and trailed 5-2 in the first set. But Stephens saved three set points before dominating the tiebreaker.
"I let out some screams, which I normally don't do," Stephens said about her slow start. "I am just happy to get through."
Stephens went 3-1 up in the second set before Petkovic reeled off 10 straight points to turn it around.
Stephens managed an early break in the third and the Australian Open semifinalist closed out the victory on her third match point.
Stephens faces Stefanie Voegele of Switzerland, who rallied past Karin Knapp of Italy 4-6, 6-2, 7-5 to advance to her first quarterfinals since April.
Earlier, Dominika Cibulkova of Slovakia routed Katarzyna Piter of Poland 6-0, 6-1 in 52 minutes. Piter, playing in her first main draw of the year, broke the seventh-seeded Cibulkova in the second set for her only game.
In her fourth quarterfinal of the season, former finalist Cibulkova will take on two-time former champion Ana Ivanovic.
Also, Patricia Mayr-Achleitner of Austria missed two match points at 5-3 in the second set before defeating Maryna Zanevska of Ukraine 6-1, 6-7 (1), 6-4 to set up a quarterfinal against top-seeded Angelique Kerber or Alexandra Cadantu of Romania.