Pattaya: Sania Mirza dug deep into her reserves to overcome a fighting Anne Keothavong 6-4, 7-5 to progress to the singles quarterfinals of the $220,000 Pattaya Open here on February 9.
The unseeded Indian, ranked 111, tamed the giant-killing British rival in a hard-fought second round match after an hour and 40 minute struggle.
Keothavong, ranked 88, had shocked second seed and world number 16 Dominika Cibulkova of Slovakia in the opening round.
Sania has also reached the doubles quarterfinals with Australian partner Anastasia Rodionova.
The top-seeded pair routed the hapless French pair of Iryna Bremond and Caroline 6-0, 6-2 in the first round.