Eugenie Bouchard edged out Venus Williams in another hard-fought encounter between the two to progress through to the quarter-finals of the Family Circle Cup in Charleston.

In their only previous meeting, Williams clinched a three-set victory in Japan last year in a match that lasted over three hours, but this time it was 20-year-old Canadian Bouchard who emerged victorious after another lengthy clash.

The sixth seed won through 7-6 (8/6) 2-6 6-4 in two hours and 14 minutes to seal her place in the last eight for the second successive year.

"In the second set she really started going for her shots. I just tried to keep fighting," Bouchard said after the match.

"It's always fun for me to play against such a great champion like Venus. She's still playing at such a high level and it was such a battle out there."

In other matches involving two seeds, number four Sabine Lisicki suffered a surprise 6-1 6-0 mauling at the hands of fellow German Andrea Petkovic, the 14th seed, while number nine Lucie Safarova recovered from a set down to defeat seventh-seeded Samantha Stosur 3-6 6-4 6-4.

Also, second seed Jelena Jankovic progressed through with a 7-5 6-1 triumph over Ajla Tomljanovic, and joining her in the last eight where third-seeded Sara Errani and number 12 Daniela Hantuchova following their respective wins over Shuai Peng and Teliana Pereira.

Hantuchova now faces an all-Slovakian showdown with Jana Cepelova, who followed up her upset victory over Serena Williams earlier in the week with a 7-6 (7/4) 3-6 6-3 triumph over 13th seed Elena Vesnina.

Swiss qualifier Belinda Bencic was the other player to go through after beating Elina Svitolina.