Third-seeded and defending champion Petra Kvitova fought back for an opening-round victory, while second-seeded Angelique Kerber went by way of a second-round upset Tuesday at the New Haven Open, a final U.S. Open tune-up.

Former runner-up Elena Vesnina of Russia upended the left-handed German Kerber in 6-2, 6-4 fashion on the hardcourts at the Connecticut Tennis Center at Yale University. Vesnina reached the final here in 2009.

Meanwhile, the Czech slugger Kvitova came from behind to beat German lucky loser Annika Beck, 4-6, 6-3, 6-3.

The former Wimbledon champion Kvitova beat Russian Maria Kirilenko in last year's New Haven finale. She'll face American qualifier Alison Riske on Wednesday.

Anastasia Pavlyuchenkova was another unlikely winner Tuesday, as the Russian earned a 7-5, 6-3 win over seventh-seeded Sabine Lisicki, last month's Wimbledon runner-up to since-retired Marion Bartoli.

In other second-round play, Czech veteran Klara Zakopalova topped Puerto Rican qualifier Monica Puig 6-4, 6-1 to reach the quarterfinals, where she'll face Vesnina.

The 2013 New Haven titlist will earn $117,000.