It wasn’t the only shocker of the day, as Spanish veteran David Ferrer rallied to beat world number three Alexander Zverev 2-6, 7-5, 6-3 to reach the third round.
Ferrer, 36 and ranked 155th in the world, received a wild card into the tournament as he continues a limited schedule in a 2019 billed as his farewell tour.
Zverev, runner-up to John Isner here last year, coughed up 12 double faults as he suffered his second straight early exit in succession after a third-round departure at Indian Wells.
Osaka was coming off a fourth-round exit at Indian Wells, but Hsieh’s coach said her victory wasn’t all that surprising.
“She has enough experience to stay strong and you saw that,” French coach Frederic Aniere, who has worked with Hsieh for the last two years and is also her boyfriend, told AFP.
“Yes it’s huge, but for her it’s not a big surprise.”
Osaka’s second-round win over Belgian Yanina Wickmayer on Friday saw a second set wobble from the two-time Grand Slam winning star and it was more of the same against Hsieh, who simply refused to give up the fight.
“I was kind of immature because I was thinking too much, like everything was on my racquet,” admitted Osaka. “I got ahead of myself.
“Of course I want to win every match and I think I have dealt with people always asking me if I am going to win because I have number one next to my name,” added the Japanese star.
“I thought I was doing fine with that but I guess I am not.”
Injured Serena withdraws
The 33-year-old Hsieh will play Caroline Wozniacki in the fourth round of the women’s draw, which now looks wide open following Osaka’s defeat and former world number one Serena Williams’s surprise exit with a left knee injury.
The American has completed just seven matches this year, withdrawing in Indian Wells with illness midway through a round of 32 match with Garbine Muguruza.
There are surely doubts now that the 37-year-old can add to her tally of 23 Grand Slams, something which has so far proved beyond her since returning last year after taking time out following the birth of her first child.
With Williams out, Wang Qiang, the 18th seed from China, advances to the fourth round on a walkover.
In the late game, unseeded Canadian Bianca Andreescu beat Angelique Kerber for the second time in a week 6-4, 4-6, 6-1, outlasting the German eighth seed in a two hour, nine minute three setter.
The duo also met in the WTA Indian Wells final, with Andreescu winning 6-4, 3-6, 6-4.
