Unseeded lefthander Sowjanya Bavisetti and second seeded Prathana Thombare also made it to the last four with contrasting wins.
In the quarterfinals, sixth seed Bhambri, ranked 593 currently, played attacking tennis in the second and the thrid set to topple top seeded Ankita 4-6,6-2,6-3 in a match that lasted for two hours and 15 minutes.
In the second set, Prerna dominated the game with some attacking tennis breaking Raina twice to win the second set 6-2 and force the third set.
In the decider, both players held on till 3-3 when Prerna broke Ankita to go up 4-3. She then held on to her serve to take the score to 5-3.
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In the 9th game, Bhambri led 0-40 , but Ankita showed signs of comeback making it duece, but lost two points again to falter and give Bhambri her first win over Raina in the last eight months.
"I lost to a better player today," said Ankita.
In another upset match, eighth seeded Nidhi Chilumula scored a rather easy 6-3,6-3 win over third seeded and 515 ranked Rishika Sunkara in an hour and 45 minute tussle to make it to the last four stage.