Sania Mirza turned on the heat again at the SAAP stadium in Hyderabad on Wednesday to upset fourth seed Zie Zheng of China in the second round of the WTA Hyderabad Open.

The victory gave the Indian wildcard a berth in the quarter-finals of the tournament for the first time.

With the Maratha Warriors hockey team and former India cricket captain Mohammad Azharuddin cheering her, Mirza braved an injury to win 6-1, 2-6, 6-3.

The 18-year-old twisted her right ankle at 2-3 down in the second set and received medical assistance on court. In the next game her serve was broken and she eventually lost the set 2-6.

"My left ankle was already injured and when I twisted the right ankle all sorts of things started coming to my mind. I thought I would be out of the tournament and lost my concentration a little bit. After the injury I was thinking of closing out the points early and avoid running," said Mirza after the match.

The Chinese girl was stunned by Mirza's power in the first set, in which she won just one game. But on winning her third service game of the match in the second set, Zheng, ranked 61st, regained confidence and had the local girl on the run.

Hampered by the injury and self-doubt, the Indian ace surrendered meekly in the remaining games as the Chinese took the set 6-2.

"I was already down 5-2 so I didn't want to stress myself in the second set," admitted Mirza.

But a break of serve in the first game of the third set spurred the Indian. She dominated the rallies and whatever Zheng did, she did better. Her forehand regained its edge and Zheng was completely outplayed as Mirza closed the chapter without much fuss.

The third set was interrupted at 30-30 in the sixth game when six bulbs in the floodlight pylon went out. After a brief halt, Tour supervisor Clare Wood had the game restarted under reduced light after consulting the two players.

Mirza will play Israel's Tzipora Obziler in the quarter-finals. Obziler crushed Evie Dominikovic of Austria 6-3, 6-2 earlier in the day.

"Obziler is a seasoned player and though she's ranked 115th I will not take her lightly. This was my biggest win, since Zheng is the highest ranked payer I have defeated. But the numbers don't really matter," said Mirza.

The Israeli, who will play her first match on centre court on Thursday, was apprehensive about the noise from the stands, saying it could be distracting for the players.