Seventh-seeded Rybarikova of Slovakia breezed to a 6-0, 6-2 victory over third-seeded Russian Ekatarina Makarova in the day's first semifinal, winning her ninth consecutive match in Washington.
She'll next take on Germany's Petokovic, who upended fourth-seeded Frenchwoman Alize Cornet 7-5 6-3 in a rain-delayed second semifinal.
Petkovic will be playing in her second WTA final of the year.
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UPI Sports Results for September 20, 2014