Germany's Mona Barthel advances at Quebec City

Mona Barthel surprised defending champion Barbora Zahlavova Strycova cruising to victory in straight sets 6-3, 6-4 in the quarter-finals of the WTA Tour's Bell Challenge tournament on Friday.

The 22-year-old German third seed hammered four aces and had to overcome seven double faults in the 87-minute match on the indoor carpet at the PEPS Laval University facility.

Czech player Zahlavova Strycova, who beat Kiwi Marina Erakovic in last year's final, finished with four double faults and won less than half (42 percent) of her second serve points.

Barthel advances to the semi-finals where she will face Kirsten Flipkens of Belgium, who was leading Anna Tatishvili 6-2, 3-0 when the Georgian retired from their match.

Flipkens upset top seed Dominika Cibulkova in the opening round.

In other quarter-finals Friday, France's Kristina Mladenovic routed American Melanie Oudin 6-0, 6-1 in just 63 minutes.

Mladenovic will next square off against eighth seeded Lucie Hradecka for a place in the final. Czech Hradecka cruised past Lauren Davis of the United States 6-4, 6-2 in their quarter-final match.