Andrea Petkovic secured a 6-2, 6-1 win over American Sloane Stephens on Friday to reach the semi-finals of the WTA San Diego Open.
The 23-year-old has become the sixth German to break into the WTA Top 10.
She next faces third-seeded Pole Agnieszka Radwanska.
Russia’s Vera Zvonareva fended off Sabine Lisicki of Germany, earning a 6-3, 3-6, 6-4 win on her fifth match point.
The top-seed will now play a resurgent Ana Ivanovic, who came from 1-4 down in her opening set to defeat China’s Pen Shuai 6-4, 6-2.
The Serb fifth seed has been working with a new coach and trainer which commentators say is starting to pay dividends.