The third-seeded Williams recovered from a mid-game slump to win 6-4, 4-6, 6-0 on Thursday evening.
She is now the highest ranked player left in the competition, reports EFE news agency.
She will play Maria Sakkari of Greece in the quarter-finals.
The tournament is being played at the San Jos? State University Tennis Center.
The event is a ladies-only competition, including singles and doubles, with total prize money of $799,280.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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