The fifth-seeded Capriati, who had lost eight straight matches to Williams, won 6-4, 6-4. Mauresmo, the No. 2 seed, eliminated Russian Vera Zvonareva 6-2, 6-3.
Mauresmo has beaten Capriati six times in the 10 matches they have played.
Capriati had a 5-1 lead in the second set, lost her serve on match point and Williams closed to 5-4. Capriati then held serve for the win.
The American, seeking her 15th career title, has not been in a final match since she won at New Haven, Conn., last August.
Mauresmo made it to her fourth final of the year. She won her 11th title in last week's Ladies German Masters in Berlin.
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