Two days after winning the title in Hiroshima, Nao Hibino had to open the campaign in Osaka and it didn't go well for her, losing to Varvara Flink 6-4, 7-5 in an hour and 39 minutes. The Russian served at 47% but drew the most from her initial shot, fending off eight out of ten break chances and delivering four breaks that propelled her into the next round.
Hibino kicked off the encounter with a break although she couldn't stay in front for too long, suffering breaks in games three and five to send Flink ahead, with the Russian saving a break point in game ten for a 6-4.
In set number two, Hibino erased a 5-3 deficit to climb back to the scoreboard in the very last moment before getting broken again in game 11, allowing Varvara to fend off a couple of break chances in the next game and advance into the next round.
Yulia Putintseva took down a lucky loser Katarzyna Kawa 6-4, 7-6 in an hour and 46 minutes, taking half of the return points and delivering five breaks from six opportunities. Yulia opened a 4-1 advantage in the first set and closed it with a hold in game ten before more challenging set number two where they traded breaks three times.
Putintseva served for the win at 5-4 but got broken at love to keep the Pole in contention until the tie break where Kawa had a 4-0 lead. Staying focused, Yulia rattled off seven straight points to move over the top and avoid the deciding set.
Su-Wei Hsieh saved a match point in a 3-6, 7-6, 6-1 triumph over the struggling Spaniard Garbine Muguruza in just over two hours, overcoming a 6-3, 3-1 deficit and repelling that ultimate chance for Garbine in the 12th game of the second set to gain massive momentum.
Su-Wei claimed the tie break 7-1 and it was all about her in the decider, delivering three breaks in a row to leave the rival behind and advance into the second round. The 5th seed Madison Keys took down Daria Kasatkina 6-3, 6-4 in an hour and 15 minutes, serving at only 46% and getting broken four times.
To erase that deficit, Madison stole 56% of the return points and claimed six breaks from ten chances, rattling off 16 of the last 19 points in the first set and shifting into a higher gear from a 3-1 down in set number two with three straight breaks that propelled her over the top.
The 7th seed Donna Vekic toppled Caroline Garcia 7-5, 6-2 in an hour and 54 minutes, beating the French player for the fourth time in eight encounters. The Croat hit ten double faults but was at her best when it came to the pivotal points, saving nine out of ten break chances and earning four breaks to seal the deal in straight sets.
The opening set lasted for an hour and Vekic grabbed the last three games from a 5-4 down, controlling the pace in set number two with breaks in games one and five and bringing the encounter home to reach the second round.
Hiroshima finalist Misaki Doi needed just 54 minutes to dismantle Kristina Mladenovic, dropping only 11 points on serve and repelling all three break chances to mount the pressure on Mladenovic who couldn't endure it, spraying too many errors and losing serve four times to end her run in the first round.