Williams, the top seed, rolled to a 6-2, 6-1 victory over Silvia Farina-Elia of Italy, while the fifth-seeded Seles posted a 6-4, 6-3 triumph over Justine Henin of Belgium.
Williams will face third seed Amelie Mauresmo of France in the semifinals on Saturday. Seles will go up against Jelena Dokic of Yugoslavia in the final four.
Starting 2002 by capturing the Gold Coast title, world No. 2 Williams saw her winning streak against top-10 opponents end at 15 matches in the quarterfinals of the Australian Open, falling to Seles.
Williams has beaten Mauresmo in their two previous meetings, including their encounter in the Round of 16 at Melbourne.
Mauresmo, the defending champion here, reached her first semifinal of the year by overwhelming Francesca Schiavone of Italy, 6-2, 6-2.
The 22-year-old took the title here after losing in the final a year earlier to Williams' sister, Serena.
Seles, 28, reached the final of this event in her only previous appearance in 1993. She lost in the final to Martina Navratilova.
The former world No. 1 also advanced to the semifinals at the Australian Open, falling to eventual runner-up Martina Hingis.
Dokic rallied to beat Elena Dementieva of Russia in the quarterfinals of the Open Gaz de France, 5-7, 6-1, 6-2. She bounced back after losing in the second round of the Toray Pan Pacific Open -- her first outing of 2002.