HIROSHIMA, Japan - No.1 seed Hsieh Su-Wei was stretched to three sets in her opener at the Hana-Cupid Japan Women's Open by the indomitable wildcard Risa Ozaki, but pulled through 6-1, 3-6, 6-3 in one hour and 56 minutes to move into the second round.

The defending champion, who picked up her third career title here last year after defeating Amanda Anisimova in the final, once again looked perfectly at home on the Hiroshima courts as she sped through a one-sided first set, but was ultimately forced to summon all her focus - and a few touches of magic - to emerge on the winning end of a tussle that was tightly contested by Ozaki until the bitter end.

"I was thinking there would be a lot of pressure as the defending champion," mused Hsieh afterwards. "But I was really relaxed and tried to enjoy the match... but the first match is never easy, I was trying to find my rhythm."

Hsieh's inimitable 'Su-Wei style' was on display from the off as the 33-year-old conjured up a sliced, angled off forehand volley en route to an immediate break. Once she had fended off four points for the break back in the subsequent game, Hsieh would find the rest of the set smooth sailing, finding both angles and power on brilliantly timed aggressive returns to outmanoeuvre the Japanese World No.292. Characteristically, a nonchalantly flicked dropshot would seal the set for Hsieh.

Though Ozaki managed to grind out a couple of holds as the second set got under way, Hsieh remained in the driver's seat - and when she carved out the first break point for a 4-2 lead, seemed on the brink of wrapping up the win. But Ozaki, a former World No.70 competing in a WTA main draw for the first time since Monterrey 2018 and looking for her first win at this level since the 2017 US Open, showed some impressive resilience, buckling down to keep her baseline game watertight. A forehand winner fended off that break point - and was the beginning of a four-game run for the 25-year-old.

Loading up her groundstrokes with topspin and maintaining impeccable depth, Ozaki kept Hsieh at bay efficiently: forced to create her game out of nothing, the Auckland and Dubai semifinalist lapsed into error. The local player would also hold her own in several of the finesse exchanges that Hsieh often dictates: a counterdrop paved the way to Ozaki's first break of serve in the seventh game, a sliced winner down the line helped her extend the lead to 5-3, and a high volley following a Hsieh dropshot sealed the set and an unlikely turnaround.

"Often happens when I win one set!" laughed Hsieh afterwards. "I lose a little bit of concentration - I need to fix this."

A refocused Hsieh did indeed fix it today, asserting her authority as the decider got under way - beginning with a dropshot-lob combination and featuring a number of cheeky dropshot return winners. The World No.29 reeled off 12 of the first 14 points and built a 4-0 lead that would ultimately prove unassailable.

Not that Ozaki didn't give another fightback her best shot: chasing everything down determinedly, the 2016 Nanchang semifinalist would capture the Hsieh serve twice more. But both times, the higher-ranked player would come up with her best tennis to regain her lead, seizing victory on her first match point with another marvellously angled crosscourt winner.

Although Hsieh pulled through, No.4 seed Anastasia Potapova was unable to avoid the upset, falling 6-7(4), 6-4, 6-4 to Australian qualifier Zoe Hives in a torrid two-hour, 51-minute marathon. The Russian committed 15 double faults across a match that featured 16 breaks of serve, while World No.163 Hives would strike six aces en route to a career-best win - and the third Top 100 scalp of her career.

Meanwhile, former World No.56 Nao Hibino gave the home crowd something to cheer about by pulling through another epic 6-7(2), 7-6(5), 7-5 over teenage Canadian qualifier Leylah Fernandez. The 17-year-old Roland Garros junior champion served for the match at 5-4 in both the second and third sets, but Hibino's never-say-die attitude enabled the Japanese player to come up with her finest shots with her back to the wall - and her first WTA main draw win since Monterrey in April after two hours and 54 minutes.

Elsewhere, Patricia Maria Tig's comeback from maternity leave continued apace: having come through qualifying, the Bucharest runner-up and Karlsruhe 125K champion progressed past 21-year-old wildcard Ayano Shimizu 6-4, 6-2 to set up a second-round clash against No.8 seed Laura Siegemund, who overcame Russian qualifier Valeria Savinykh 6-4, 6-1. No.7 seed Sara Sorribes Tormo was another favorite to avoid the upset, fending off Sorana Cirstea 6-2, 3-6, 6-2; the Spaniard will now face Russia's Varvara Flink, who moved past Kristina Kucova 6-3, 6-2.

Former World No.20 Mihaela Buzarnescu was another success today. The Romanian, who has sunk to World No.125 following an extended slump following an ankle injury she suffered in Montréal last year, took a step towards rebuilding her ranking with a 6-1, 6-4 victory over Bulgarian qualifier Viktoriya Tomova. Meanwhile, an all-Japanese derby saw former World No.30 Misaki Doi mount a stunning comeback against 37-year-old qualifier Junri Namigata. The veteran, who played her first WTA main draw in 2005 and reached a career high of World No.105 in February 2011, held a 40-0 lead as she served for the match at 5-4 in the second set - but Doi stormed back from the brink, saving all three consecutive match points for a 4-6, 7-5, 6-2 win in two hours and 25 minutes.