Serena Williams beat fifth-seeded Jelena Jankovic 6-2, 6-2. She won two-thirds of the points on serve and saved four of the five break points Jankovic had.
Serena Williams also finished off half of her own 10 break chances while winning 53 percent of the points when receiving serve.
Venus Williams, unseeded this week, claimed a 6-3, 7-5 decision over Flavia Pennetta with three breaks in each set. She won more than half (33-of-64) of the points off Pennetta's serve on overcoming a total of four dropped service games.
No. 8-seeded Caroline Wozniacki had little trouble beating Sorana Cirstea 6-1, 6-2 in 62 minutes in her quarterfinal. Wozniacki took 63 percent of the points in the match and ended up with five breaks in Cirstea's seven games serving.
Venus Williams is 4-0 in her career versus Wozniacki, although Friday's semifinals will be the first time they've played since 2008.
If the Williams sisters both win Friday, Saturday's tournament final would be the 25th career meeting between the two. Serena Williams holds a 14-10 series edge, having won the last four pairings. Eleven of the previous 24 matches have been in tournament finals.