But Hsieh Su-Wei is also in the Australian Open quarter-finals and not without a shot of taking down three-time grand slam champion Naomi Osaka on Tuesday.

"Osaka is a super player. The good thing is Su-Wei has beaten her before and Naomi won't have forgotten that," Hsieh's Australian coach Paul McNamee told AAP.

"Every match is different but Su-Wei is really hitting the ball well and is in a good place."

Statistically, Taiwan's greatest-ever tennis player is in the best place of her career, the oldest first-time grand slam quarter-finalist in the 53-year open era and the world's top-ranked doubles player.

Yet staggeringly, she can't pick up a sponsor.

"It's too late," McNamee said.

"She's 35. She's not thinking about that anymore. She's not interested.

"At one stage it hurt her a bit that no-one wanted her, but now she accepts it.

"I remember we had to go and buy her equipment for the (2019) Wimbledon (doubles) final. I mean, what I'm wearing now she bought for me as a present.

"She goes shopping to buy tennis clothes a couple of times a week.

"She doesn't have any contracts at all. That's why she's like Times Square on the court with the different logos from the different companies."

But McNamee wouldn't change a thing about the bubbly veteran and says it's that carefree approach to life that makes Hsieh so special.

"She's a free spirit," he said. "There's only one Su-Wei.

"It's important that she's allowed to express herself. That's the same with her tennis. She kind of acts on a whim sometimes, doesn't like to plan too far ahead."

Despite lacking any big weapons, the world No.71 boasts a wild 8-2 win-loss record over top-rivals and is so gifted, says McNamee, that it's mind-boggling.

"She's so precise the way she plays," he said.

"No one can redirect traffic as well as she can on both sides. Doesn't matter which way it's coming from, she can redirect it either way."

As a ball striker, McNamee hasn't seen anyone better.

"We had a bit of trauma before this tournament because she had to get a restring before the tournament. That's once a year," he said.

"Players change racquets on the change of balls, right? She'll go years with the same racquet.

"One of the reason is she hits the ball so purely in the centre of the racquet. Most people break strings when they hit it around the frame. She doesn't frame balls. I mean, she would rather not play if she did that."

Australian Associated Press