Williams, who won her 40th career singles title in Dubai last week, will face defending champion Flavia Pennetta for the title.
Pennetta reached her sixth consecutive final at the Mexican Open with a 6-3, 6-3 victory over 2004 champion Iveta Benesova.
“Six finals is incredible. I didn’t expect it or hope for it,” said Pennetta, who is trying to win her third Acapulco title in five years. “Every year I come just hoping to play good tennis and produce a little magic for myself.”
The second-seeded Pennetta has won three of her five career matches against Williams, including their only match on clay in the third round of last year’s French Open.
Benesova beat Pennetta in the 2004 final but the Italian served better on Friday, and created more chances than Benesova could produce. Pennetta claimed four of eight break points and lost her serve only once to the fourth-seeded Czech.
Pennetta, who improved her Acapulco record to 28-4, won the title in 2005 and 2008.
“I think I am more famous here than in Italy, this is like my second home,” she said.
Nicolas Almagro of Spain also will get to defend his title in the men’s final. He defeated unseeded Martin Vassallo Arguello of Argentina 6-4, 6-4. Fourth-seeded Almagro will play for his fifth career title against either second-seeded Gael Monfils of France or fifth-seeded Jose Acasuso of Argentina.
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