Both sisters had to win twice Friday to earn their semifinal berths, a task made necessary by day-long rains that wiped out half of the schedule Thursday.
The top-seeded Serena Williams defeated Mallory Burdette 6-4, 6-2 and then breezed past sixth-seeded Lucie Safarova 6-4, 6-1.
Venus Williams, seeded fifth in this event, took out Varvara Lepchenko 6-2, 4-6, 6-2 and then defeated Madison Keys 6-4, 6-4.
The sisters will be meeting for the 24th time with Serena holding a 13-10 advantage. They have not met, however, since the 2008 Tour Championship -- an event that saw Serena defeat Venus twice.
Twelve of their career matches have come in Grand Slam tournaments.
The other semifinal will send Jelena Jankovic against Stefanie Voegele, both of whom had to play just one match Friday.
Jankovic was a 6-2, 6-1 winner over Eugenie Bouchard and Voegele surprised second-seeded Caroline Wozniacki 3-6, 6-4, 6-3.
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