Reigning US Open tennis champion Sam Stosur suffered a blow ahead of her title defence in New York later this month when she lost to Lucie Safarova in the third round of the Rogers Cup in Montreal.
Just over two weeks from the start of the last grand slam of the year, the Australian fourth seed went down in two tie-breaker sets to the Czech.
Stosur, who lost to American Serena Williams in last year's Montreal final, had big problems with her second serve, winning only 37 per cent of the points on her second delivery in the entire match.
Meanwhile, fifth-seed Petra Kvitova of the Czech Republic reached the quarter-finals with a 6-1 6-1 defeat of France's Marion Bartoli.
Sixth-seeded German Angelique Kerber stopped Ekaterina Makarova of Russia 6-3 6-3 and Caroline Wozniacki of Denmark ousted Kiki Bertens 7-5 6-1.
