PONTE VEDRA BEACH, FL, USA - Defending champion Caroline Wozniacki led the winners' list at the MPS Group Championships on Tuesday, but the seeds didn't emerge entirely unscathed on the second day of the $220,000 International event.

The main casualty was No.2 seed Alona Bondarenko of Ukraine. Bondarenko, who began the season by capturing her second Sony Ericsson WTA Tour singles title at Hobart and reaching the round of 16 at the Australian Open - a run that included a win over Jelena Jankovic - has now lost four openers in a row. After winning a tight second set against Olga Govortsova, the 25-year-old slumped to defeat against the Belarusian, 63 46 60.

Read Govortsova's 'Getting to Know' interview from earlier in her career.

As well as top-seeded Wozniacki, who held off a second set surge by Swiss veteran Patty Schnyder to advance, 60 64, Elena Vesnina and Melanie Oudin were the other seeds moving through with straight set wins. Vesnina, seeded fourth, beat Australian qualifier Sophie Ferguson; after letting a 5-2 first set lead slip, Oudin eased to a 75 62 win over Rossana de los Ríos of Paraguay.

Peng Shuai, Angelique Kerber and Julia Goerges also went through to the second round, and it was a good day too for a couple of the qualifiers. Bethanie Mattek-Sands outlasted Anastasia Rodionova, 7-5 in the third set, while Anna Tatishvili upset Magdalena Rybarikova by a similarly tight scoreline.

Lucky loser Varvara Lepchenko edged recent Bogotá champion Mariana Duque Marino in a second set tie-break, while Japanese wildcard Ayumi Morita beat qualifier Sesil Karatantcheva in three.