The United States-based Japanese player fought through a challenging quarterfinal to dispose of gallant young American Hailey Baptiste 6-7 (2-7), 6-1, 6-2 at the Manuka Doctor Arena.
However the Auckland weather made for a challenging day, with play interrupted by rain multiple times, and final heavier showers stopping play with top seed Madison Keys up 4-3 in the second set after losing the first set to Denmark’s Clara Tauson.
The winner will take on 20-year-old Robin Montgomery, who had earlier edged out experienced fellow American Bernarda Pera 6-4, 6-4.
There were six Americans contesting the quarterfinals, the most from one nation in WTA history.
Osaka struggled to manage the power of the 23-year-old Baptiste, who had only got to bed in the early hours of yesterday after a marathon battle to edge out British lucky loser Jodie Burrage 5-7, 7-5, 7-6 in a monumental clash.
In fact Osaka was not aware of who her opponent would be when she herself went to bed, and realised it was therefore a lengthy match.
Baptiste, who made an early name for herself after accounting for Keys in her WTA debut in the 2019 Washington Open, displayed a mix of power and purpose in the long battle with Burrage.
She showed little indication of her exertions in claiming the opening set against Osaka, winning 7-6 in the tiebreak. It woke up the seventh seed Osaka, who took the game to another level, battling a rain delay and a lengthy injury break for Baptiste before securing her win.
"I feel really happy. It is my first semi since I started playing again. Even though it was a three-set match, I was able to pull through in the end," said Osaka.
"I struggled a lot last year with not producing results. To come out today with a bang in the first tournament of the year for me proves there is a continuation of the growth."
She had time to write in her notebook during the break, reminding herself to play in the manner in which she wants to perform in Melbourne, despite the result.
"So I kept going for the shots that I know I will have to make there.
"I felt bad for her to have an injury at the start of a new season and honestly, I would have preferred a longer match than a shorter one."
Osaka has been a magnet for fans this week, with a packed crowd in for her match today and fans waiting for photos and autographs.
"When I am told that people look up to me, then I feel a lot of responsibility. I realise I have not been the greatest role model at times but I am learning and trying my best.
"Of course, I am sad that my great role models Serena and Venus [Williams] are not around, so I hope I am able to play as many years as them and build a good foundation to the sport."
Twenty-year-old Montgomery progressed with a 6-4, 6-4 victory over compatriot Bernarda Pera, an experienced American with a career high No 27 in the rankings.
By Ian Hepenstall
