The Williams sisters remain on course for another meeting after booking their places in the quarter-finals of the Bank of the West Classic at Stanford.
Wimbledon champion Serena took her winning streak to nine matches with a straight-sets defeat of Hungary's Melinda Czink.
The top seed won 6-3 7-6 to set up a clash against Austrian left-hander Samantha Stosur.
Second seed Venus, beaten by her sister in the final at SW19 earlier this month, reached the last eight with a 6-3 7-5 win over Russian qualifier Alla Kudryavseva.
Blocking her path to the semi-finals is former world number one Maria Sharapova, who is continuing her comeback from shoulder surgery.
Eighth-seed Marion Bartoli progressed with a 7-5 6-4 victory win against American qualifier Melanie Oudin.
Next up for the Frenchwoman is Serbia's Jelena Jankovic, as a result of the fourth seed's 2-6 6-2 6-4 defeat of Germany's Sabine Lisicki.