Seeds tumble in New Haven
Angelique Kerber and Sabine Lisicki were surprise second-round casualties at the New Haven Open.
Second seed Kerber slumped to a 6-2 6-4 loss to Elena Vesnina, with the unseeded Russian now set to face Klara Zakopalova.
"She's a very tough player, can win on any surface and is a fighter, so it was important for me to get early confidence by winning the first set," said Vesnina, who was a runner-up at the event in 2009.
"The second set was up and down with a lot of breaks, but at the key moments I served well."
Lisicki, the No 7 seed, was also beaten in straight sets by a Russian - with Anastasia Pavlyuchenkova registering a 7-5 6-3 win.
Third seed Petra Kvitova got her title defence off to a stuttering start with a 4-6 6-3 6-3 first-round victory over Annika Beck.
Kvitova had looked on course for an early exit as she trailed by a set and a break but she rallied brilliantly to set up a clash with qualifier Alison Riske.