Resilient Thai fifth seed Luksika Kumkhum caused the biggest upset at the L&T Mumbai so far as she fought back from a set down to knock out top seed and world No 47 was Zheng Saisai in the quarter-finals on Friday.

Kumkhum, with her unusual double-handed forehand, played lights out tennis to notch up a 3-6 6-4 6-4 victory in 2 hours and 17 minutes at the Cricket Club of India, admitting that she was happily surprised to reach the last four at the $125K WTA event.

Saisai’s exit meant three out of the four top seeds have been ousted before the semis, after American third seed Sachia Vickery retired and Serbian fourth seed lost in the first round.

Kumkhum will take on Russian Margarita Gasparyan, who came through in an intense battle to end the rampaging run of Danka Kovinic of Montenegro 7-6 (4), 4-6, 6-1.

However, second seed and last year’s runner-up Dalila Jakupovic of Slovenia reached the semis comfortably with a 6-2, 6-3 win over Chinese Jia-Jing Lu.

In the first match on Centre Court, Saisai won the first set with relative ease and looked all set to progress to the semis. However, Kumkhum, who was one game away from losing in the first round to India’s Pranjala Yadlapalli, battled her way back into the game with an impressive, all-court display from then on.

She was especially strong in the decider when she raced to a 5-1 lead with two breaks of serve. Saisai mounted a brief comeback when she broke back twice to narrow the lead to 4-5, but the fifth seed held her nerve and converted her third match point when serving for the match

“Sometimes you have nothing to lose and just have to find a way to win. When it’s a tough day, I don’t think about it and just keep playing,” she said of both her fightback wins in Mumbai so far.

The Chinese Top-50 player rued her missed chances in the second set saying, “The second set was pretty close. I missed a few points and she was more aggressive.

“I did not start the third set well. I picked up the pace in the end but it was not enough. I had a long season and it is difficult to play in these conditions,” Zheng added.

In the other tough quarter-finals, Russia’s Gasprayan overcame Kovinic, who had earlier beaten fourth seed Danilovic and Ankita Raina, in a tough three-setter.

The sixth seed struggled with the conditions and fluffed her chance to serve out the first set at 5-4. She needed a medical time out after losing the next games but bounced back in the tiebreaker. After a couple of long, gruelling rallies.

She seemed to have lost her way in the second set and as she 1-3 and could not recover from that one break as Kovinic served out for a decider. But the Russian, encouraged by her coach Anastasia Myskina, raced through the third set taking a 5-0 lead.

As she finally sealed her semi-final spot with an ace, she yelled a loud “come on”, an indication of how much this means to her.

“To be honest, I want to play as any tournaments as I can because I want to play in the Australian Open next year, so reaching the semis here was very important,” the world No 110, who returned from three knee surgeries just this year, said after her match.