The fourth-seeded American battled a pulled stomach muscle last year and has not won a title in 14 months. She missed the last six months of the 2003 season with the ailment, with her last match the final at Wimbledon.
Williams had struggled in her comeback as she failed to get past the quarterfinals in her previous four tournaments. She seeks her 30th career title and first since the Proximus Diamond Games at Antwerp in February 2003.
No. 16 Conchita Martinez of Spain will face Williams in Sunday's final after beating 11th-seeded Patty Schnyder of Switzerland, 6-4, 6-3.
Martinez, 32, won this event in 1994 and 1995 and needs one more title here to tie Martina Navratilova for second-most all time.