Charleston - Canadian starlet Eugenie Bouchard held off former world number one Venus Williams 7-6 (8/6), 2-6, 6-4 on Thursday to reach the Family Circle Cup quarter-finals.
Bouchard, an Australian Open semi-finalist who is seeded sixth in the green claycourt WTA premier level event, saved two set points in the first-set tiebreaker, and rallied from a break down in the third to advance to a meeting with either second-seeded Serbian Jelena Jankovic or Croatian Ajla Tomljanovic.
Williams followed her younger sister, world number one and top seed Serena Williams, out of the tournament.
Serena was stunned in her opening match by Slovakian Jana Cepelova, who followed up that big win with a 7-6 (7/4), 3-6, 6-3 victory over 13th-seeded Russian Elena Vesnina.
Cepelova will face fellow Slovakian Daniela Hantuchova in the quarter-finals. Hantuchova breezed past Teliana Pereira of Brazil 6-2, 6-3.
Venus Williams, who won the Charleston title in 2004, held two set points at 6-4 in the first-set tiebreaker, but 20-year-old Bouchard won four successive points en route to taking the set.
Williams, bounced back with a strong second set, and broke for a 2-1 lead in the third, but her unforced errors allowed Bouchard to get back in it and the Canadian broke her in the final game to seal the win.
"In the second set she really started going for her shots," Bouchard said.
"I just tried to keep fighting. It was a little bit ugly at times, but I just kept trying to fight through it."
Third-seeded Sara Errani of Italy advanced with a narrow 7-6 (8/6), 7-6 (7/5) victory over China's Peng Shuai.
Peng had a set point in each set but couldn't convert.
"It was an unbelievable match," Errani said. "All the games were very close."
Results on Thursday from the WTA Tour Family Circle Cup (x denotes seeded player):
Jana Cepelova (SVK) bt Elena Vesnina (RUS x13) 7-6 (7/4), 3-6, 6-3
Daniela Hantuchova (SVK x12) bt Teliana Pereira (BRA) 6-2, 6-3
Sara Errani (ITA x3) bt Peng Shuai (CHN) 7-6 (8/6), 7-6 (7/5)
Belinda Bencic (SUI) bt Elina Svitolina (UKR) 6-7 (4/7), 6-4, 6-1
Lucie Safarova (CZE x9) bt Samantha Stosur (AUS x7) 3-6, 6-4, 6-4
Andrea Petkovic (GER x14) bt Sabine Lisicki (GER x4) 6-1, 6-0
Eugenie Bouchard (CAN x6) bt Venus Williams (USA x11) 7-6 (8/6), 2-6, 6-4
Jelena Jankovic (SRB x2) bt Ajla Tomljanovic (CRO) 7-5, 6-1