Andrea Petkovic completed a stunning turnaround on Friday, to preserve her winning ways at the Family Circle Cup.
Showing signs of frustration throughout the first set, third seed Petkovic managed to fight back to beat qualifier Danka Kovinic 2-6 6-3 6-1 in their quarter-final in Charleston.
Petkovic has never lost a match at the WTA Premier green clay event, winning the 2014 title and withdrawing the year before when she had reached the fourth round.
But the German's perfect record was in danger of being broken as Kovinic, after trailing 2-0 in the first set, reeled off seven straight games to take full control.
Kovinic also had a point to hold for an eighth game on the spin, but Petkovic broke back to begin her resurgence - with the Montenegrin putting a forehand long on break point.
Another over-hit forehand from Kovinic sealed a break lead for Petkovic in the sixth game, and she went on to level the match.
Petkovic's experience came to the fore as she leapt to a 4-0 lead in the decider, and another Kovinic forehand error on match point sealed progression for the world number 11.
She will next meet compatriot Angelique Kerber, the left-handed fifth seed fighting past 13th seed Irina-Camelia Begu 7-6 (7-3) 7-6 (7-4).
In the other semi-final, seventh seed Madison Keys will be the American representative after she saw off countrywoman Lauren Davis 6-2 6-2.
Keys will take on qualifier Lucie Hradecka, who put away an underwhelming Sara Errani - the fourth seed going down 6-2 6-4.