ANNING, China - The unseeded Ankita Raina sprung the biggest upset of the Kunming Open in the final first-round match, stunning No.3 seed Samantha Stosur 7-5, 2-6, 7-5 over an arduous two hours and 49 minutes.

The Indian No.1 showed remarkable tenacity to overcome an erratic Stosur for the first Top 100 win of her career at the 11th attempt, twice coming from a break down in the first set and closing the decider out after twice being pegged back from a break up.

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World No.77 Stosur, fresh off a Fed Cup high in which she had partnered Ashleigh Barty to score a thrilling deciding doubles rubber over Victoria Azarenka and Aryna Sabalenka to send Australia into the first final in 26 years, suffered something of a comedown in China. The 35-year-old committed 18 double faults in total, including two in all but one of her service games in the opening set.

Though Stosur was able to come through a six-deuce hold and a seven-deuce break to lead 2-0, Raina doggedly stuck with her as the Australian's game oscillated wildly, and nabbed the key break when Stosur double faulted to fall behind 5-6.

The 2011 US Open champion got her serve under control in the second set, delivering only one double fault, and was able to take it comfortably as Raina began hitting out impatiently towards its close. But the double faults and forehand shanks returned with a vengeance in the decider.

Though nervy play from Raina saw her breaks at 1-0 and 4-3 evaporate, the 26-year-old nonetheless held firm, nailing a few crucial passing shots to keep herself in the match. The World No.178's forehand had itself been somewhat unreliable over the course of the match, but in its closing stages Raina rose to the occasion to go for more aggressive plays, breaking for 6-5 with a forehand winner down the line.

Raina, fresh off her second ITF W60 final in Istanbul two weeks ago - where she lost to Vitalia Diatchenko - was able to close her career-best win out on her third match point after another Stosur forehand sailed long, setting up a second-round tilt against 2016 champion Zhang Kai-Lin.

Elsewhere, 20-year-old Japanese qualifier Chihiro Muramatsu caused another shock, sealing her own maiden Top 100 victory with a 7-6(5), 6-4 second-round defeat of No.4 seed Zhu Lin. World No.358 Muramatsu will play fellow qualifier Kaylah McPhee in the quarterfinals after the Australian ousted American Ashley Kratzer 6-4, 6-2.

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Meanwhile, 2018 Australian Open junior champion Liang En-Shuo closed out first-round action with a 6-2, 6-3 win over wildcard Gao Xinyu, and No.2 seed Zheng Saisai avoided the upsets with an emphatic 6-2, 6-1 triumph over former World No.50 Jana Cepelova. Zheng will clash with Alexandra Cadantu in the quarterfinals after the Romanian backed up her first-round upset of No.5 seed Peng Shuai with a 1-6, 6-1, 6-1 win over qualifier Miharu Imanishi.