Wimbledon champion Petra Kvitova and Finalist Eugenie Bouchard both crashed out of the second round of the Cincinnati hard court tournament on Wednesday in a setback to their US Open preparations.Ukrainian teenager Elina Svitolina toppled third-seeded Czech Kvitova 6-2, 7-6. Bouchard went down to Russian veteran Svetlana Kuznetsova 6-4, 3-6, 6-2. Top seed Serena Williams got through safely as she defeated Australian Samantha Stosur for the second time in as many weeks, 7-6 , 7-6. Fourth seed Agnieszka Radwanska beat Japan's Kurumi Nara 6-2, 6-2.Stosur, who beat Williams in the 2011 US Open final, made the world number one fight for her win. German Angelique Kerber, the sixth seed, advanced against Ekaterina Makarova 6-4, 6-1 while Italian 13th seed Flavia Pennetta beat Taylor Townsend of the US 6-4, 6-3 to set up a clash with Williams. Sabine Lisicki, the 2013 Wimbledon runner-up, beat Italy's Sara Errani, the 14th seed, 6-4, 2-6, 7-6.