Unseeded Isha Lakhani recorded the biggest upset of her career when she ousted Junior Wimbledon doubles champion and seventh seed Sania Mirza on way to the women's singles semi-finals in the $25,000 NSCI-ITF women's tennis tournament in Mumbai on Thursday.

The diminutive Mumbai lass played an attacking game, always rushing to the net, to emerge a worthy 6-3, 1-6, 6-2 winner.

The match, which lasted an hour and 26 minutes, saw Isha race to a 4-2 lead in the first set, with a break in the fifth game. Though Sania tried hard, she could not prevent her opponent from winning the set at 6-3.

In the second set, Sania came out firing on all cylinders and within no time established a 5-1 lead with breaks in the second and fourth games before serving out the set 6-1.

The match was set for a nail-biting finish. Isha effected the first break in the fourth game of the decider to go 3-1 up and held serve for a 4-1 lead. The Hyderabad girl fought back with some deep serves but couldn't hold serve in the sixth game and fell further behind at 1-5.

But Sania's experience stood her in good stead as she managed to break Isha in the seventh game to reduce the deficit to 2-5.

Isha maintained the pressure and took a 40-15 lead on Sania's serve in the eighth game. Though Sania managed to save a match-point with a deceptive drop shot, Isha took the set on the next point when the Hyderabad girl sent a return long.

In other quarter-final matches, unseeded Indian Rushmi Chakravarthi almost pulled off another upset against fourth seed Gabriala Navratilova of the Czech Republic but failed to hold her nerve in last stages of the match.

Navratilova, rallied superbly after dropping the first set 4-6, to pip the Indian 4-6, 6-3, 6-4 in one hour and 58 minutes.

Giant-killer Megha Vakharia of India, who had accounted for second seed Hana Sromova of the Czech Republic in the pre-quarter-finals yesterday, met her match at the hands of eighth seed Akgul Amanmuradova of Uzbekistan losing 6-7 (3-7), 4-6 in one hour 39 minutes.

Unseeded Montinee Tangphong of Thailand caused the second upset of the day when she sidelined her compatriot and third seed Suchanan Viratprasert 6-3, 6-2 in an hour and five minutes to fill up the last semi-final berth.

Isha will take on Tangphong while Navratilova will clash with Amanmuradova in the semi-finals tomorrow.

Results (women's singles) quarter-finals: Isha Lakhani (Ind) bt Sania Mirza (Ind) 6-3, 1-6, 6-2; Montinee Tangphong (Tha) bt Suchanan Viratprasert (Tha) 6-3, 6-2; Gabriala Navratilova (Cze) bt Rushmi Chakravarthi (Ind) 4-6, 6-3, 6-4; Akgul Amanmuradova (Uzb) bt Megha Vakharia (Ind) 7-6 (7-3), 6-4.

Doubles (quarter-finals): G Navratilova/H Sromova (Cze) bt Ankita Bhambri/Sonal Phadke (Ind) 6-0, 6-1; Sania Mirza (Ind)/S Viratprasert (Tha) bt Chantal Goombs/Karen Patterson (GBR) 6-4, 6-3; A Amanmuradova (Uzb)/Chin-Bee Khoo (Mal) 6-2, 6-2, Rushmi Chakravarti/Sai Jayalakshmi (Ind) bt Kumiko Iljima/ Ryoko Watanabe (Jpn) 6-1, 6-2.