The Williams sisters could be headed for a final matchup at the Sony Ericsson Championships after Venus advanced to the knockout rounds along with Jelena Jankovic and Caroline Wozniacki.
Venus, the defending champion, lost her first two group matches but advanced on a countback of sets thanks to Svetlana Kuznetsova's 6-3, 6-2 win over Elena Dementieva. Venus joined unbeaten sister Serena Williams in the semifinals from the Maroon Group.
Venus, Kuznetsova and Dementieva all finished with one win and two losses.
Jankovic advanced by routing a tired Wozniacki 6-2, 6-2, but the 19-year-old Dane also went through from the injury-plagued White Group when Victoria Azarenka had to retire against alternate Agnieszka Radwanska of Poland when trailing 4-6, 7-5, 4-1 in the most dramatic match of the day.
Azarenka would have advanced with a win, and served for the match twice in the second set. She needed a medical time-out early in the third to treat her left thigh and lower back. She continued playing with the thigh taped, but hobbled around the court in obvious pain, needing another time-out to treat leg cramps before the final game. She came back out, but finally called it quits while down 40-15.
Serena Williams will play Wozniacki in one semifinal today, and Venus Williams will face Jankovic at the same stage for the second straight year.