Caroline Wozniacki struggled at the start, but secured the only break in the third set.

LUXEMBOURG (AP) -- Top-seeded Caroline Wozniacki of Denmark defeated Bojana Jovanovski of Serbia 6-3, 3-6, 6-3 Friday to reach the semifinals of the Luxembourg Open.

After both players struggled to hold serve at the start, Wozniacki had the only break of the third set to clinch the win. She will face the winner of the later quarterfinal between third-seeded Sabine Lisicki and Karin Knapp.

On a day full of three-setters, Stefanie Voegele of Switzerland beat second-seeded Sloane Stephens of the United States 6-3, 3-6, 6-2, and will face Annika Beck of Germany in Saturday's semifinals. Beck came through the longest match of the tournament, defeating Katarzyna Piter of Poland, 6-3, 6-7 (3), 7-6 (5) in 3 hours, 12 minutes.

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