Sania Mirza dug deep into her reserves to overcome a fighting Anne Keothavong 6-4, 7-5 and progress to the singles quarter-finals of the $ 220,000 Pattaya Open, on Thursday.
The unseeded Indian ace, ranked 111, tamed the giant-killing Briton in a hard-fought second round match after an hour and 40 minutes.
Keothavong, ranked 88, had shocked second seed and world No. 16 Dominika Cibulkova of Slovakia in the opening round.
Sania also entered the doubles quarter-finals with Australian partner Anastasia Rodionova.
The top-seeded pair routed the hapless French pair of Iryna Bremond and Caroline 6-0, 6-2.
They are now up against the local pair of Varatchaya and Varunya Wongteanchai in the last-eight stage.
In Thursday's singles, Sania served extremely well in the second set and put behind an early break to stage a brilliant comeback.
She saved a crucial break-point in the 11th game and then broke Keothavong for the second time to claim a well-deserved win.
She now faces either Japan's Kimik Date-Krumm or Chinese Taipei qualifier Su-Wei Hsieh in the quarter-finals.