Williams defeated fifth-seeded Magdalena Rybarikova 6-4, 6-0 to continue a comeback from illness and injury that had threatened her career.
She began 2012 ranked 134th in the world, but she has climbed back to No. 20 thanks in part to a victory late last season in Luxembourg.
Olga Puchkova posted a 6-1, 6-1 victory over Jana Cepelova to set up a semifinal matchup with Williams. It will be their first career meeting.
The other semifinal will send Kristina Mladenovic, the No. 7 seed, against Monica Niculescu.
Mladenovic defeated Melinda Czink 6-4, 6-3 and Niculescu was a 6-3, 6-2 winner over Timea Babos.