Updated

Charleston, SC (SportsNetwork.com) - Jana Cepelova produced a stunning upset to highlight the second day of the Family Circle Cup tennis event, downing two-time defending champion Serena Williams in straight sets in Tuesday's second round.

Cepelova, ranked 78th in the world, won the first five games of the match en route to a startling 6-4, 6-4 victory over the World No. 1 Williams, a three- time Charleston champ and the runner up at this tournament in 2003 who was fresh off a title in Miami.

The 20-year-old Slovak scored another key break to go up 4-3 in the second set and held serve from there.

Venus Williams, herself a former Charleston champion, was able to avoid her sister's fate by outlasting Czech Barbora Zahlavova Strycova 6-3, 0-6, 7-5 in 2 hours, 18 minutes on the green clay at Family Circle Tennis Center. Venus titled here 10 years ago.

Another second-round upset came from Brazilian Teliana Pereira, who upended eighth-seeded Romanian Sorana Cirstea 3-6, 6-3, 7-6 (7-0). Seventh-seeded Aussie Sam Stosur, the 2010 Charleston champ, got past Kazakhstan's Yaroslava Shvedova 6-3, 5-7, 6-1 in second-round play.

Canadian Eugenie Bouchard, the sixth seed, had little trouble advancing to the third round after cruising to a 6-2, 6-0 decision over Russian qualifier Alla Kudryavtseva, while ninth-seeded Lucie Safarova rallied for a 2-6, 6-4, 6-4 verdict over France's Virginie Razzano.

In opening-round action involving seeds, No. 12 Daniela Hantuchova topped American wild card Shelby Rogers 7-5, 7-5; No. 13 Russian Elena Vesnina whipped Slovak Anna Schmiedlova 6-2, 6-1; No. 14 German Andrea Petkovic overcame Ukrainian qualifier Lesia Tsurenko 6-7 (2-7), 6-4, 6-1; and No. 16 Chinese Zhang Shuai fought back to beat Taipei's Su-Wei Hsieh 3-6, 7-6 (7-5), 7-6 (7-0).

Also in round one, American Vania King came back to beat Israeli Julia Glushko 4-6, 7-5, 6-3, China's Peng Shuai drubbed France's Caroline Garcia 6-2, 6-3; Lourdes Dominguez Lino erased fellow Spaniard Anabel Medina Garrigues 6-3, 6-2 and New Zealander Marina Erakovic topped veteran wild card Nadia Petrova 4-6, 6-3, 6-4.

Petrova was the 2006 Charleston champion.