MUMBAI, India -- An upset opened quarterfinal day at the L&T Mumbai Open, as No.5 seed Luksika Kumkhum of Thailand outlasted No.1 seed Zheng Saisai of China, 3-6, 6-4, 6-4, to reach the semifinals of the WTA 125K Series event on Friday.

World No.103 Kumkhum, who made the third round of this year's Australian Open for her career-best Grand Slam performance, watched a 5-1 final-set lead nearly disappear before closing out World No.47 Zheng after a nearly evenly-matched two hours and 16 minutes.

Zheng started the match as the stronger player, using exceptional court coverage and nifty passing shots to break the powerful but error-prone Kumkhum three times during the first set. The second set, however, went the way of the Thai player, as she kept up her aggression and blasted overhead putaways with aplomb, en route to tying the match at one set apiece.

The momentum stayed with Kumkhum in the decider, as she broke Zheng in the Chinese player's first three service games of the set to lead 5-1. Zheng clawed one break back, then hit two solid shots to erase match points on her serve at 5-3. But Kumkhum successfully served out the match on her second time of asking, clinching victory on her third match point after a Zheng backhand found the net.

Kumkhum will face the resurgent Margarita Gasparyan in the final four, after the 6th-seeded Russian claimed a 7-6(4), 4-6, 6-1 quarterfinal win over Danka Kovinic of Montenegro. Gasparyan dominated in the decider, winning 88 percent of her first-service points, and being gifted four of Kovinic's 11 double faults during that set.

This year, former Top 50 player Gasparyan has made a stirring comeback from injuries, winning the Tashkent Open, claiming her first Top 10 win over Kiki Bertens in Luxembourg, and climbing to her current ranking of World No.110 after starting the season unranked. This will be the first meeting between Gasparyan and Kumkhum.

In the bottom half of the draw, No.2 seed Dalila Jakupovic of Slovenia, the highest-ranked player remaining in the field, notched a 6-2, 6-3 quarterfinal victory over Lu Jia-jing of China. Jakupovic is still alive in her quest to reach the L&T Mumbai Open final for the second straight year; she fell in the 2017 championship match to last year's top seed Aryna Sabalenka.

World No.73 Jakupovic needed only 71 minutes to dispatch Lu. The Slovene never dropped serve in the match, staving off both break points she faced, and won a commanding 77 percent of points when she got her first delivery into play.

Jakupovic will meet World No.165 Irina Khromacheva in the semifinals, after the Russian beat Greece's Valentini Grammatikopoulou, 7-5, 4-6, 6-1. Khromacheva claimed victory with an error-forcing crosscourt backhand after one hour and 52 minutes of play. Jakupovic and Khromacheva have split their two previous meetings in singles.

After playing against each other in their singles semifinal, Jakupovic and Khromacheva will team up as the top seeds in the doubles event to contest a semifinal against Natela Dzalamidze and Veronika Kudermetova.