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 Thursday.
The unseeded Indian, ranked 111, tamed the giant-killing British rival in a hard-fought second round match in almost two hours.
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 a hapless French pair of Iryna Bremond and Caroline 6-0 6-2 in the first round.
They are now up against local pair of Varatchaya and Varunya Wongteanchai in the last-eight stage match. In singles, she will now face either Japanese Kimik Date-Krumm or Chinese Taipei qualifier Su-Wei Hsieh.
New-look Spain open title defence
PARIS: Alex Corretja's new-look Spain open their Davis Cup title defence against minnows Kazakhstan in Oviedo starting on Friday. They will be playing without Rafael Nadal, David Ferrer and Feliciano Lopez.
World Group 1st rd ties
Spain v Kazakhstan; Austria v Russia; Canada v France; Switzerland v USA; Czech Republic v Italy; Serbia v Sweden; Japan v Croatia; Germany v Argentina