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Down but not out: 2019 champion Naomi Osaka is still alive at the Australian Open.

The No.3 seed saved two match points to overcome two-time Grand Slam champion Garbiñe Muguruza in Sunday's fourth round, 4-6, 6-4, 7-5, to reach the quarterfinals Down Under for the second time in the past three years.

From 5-3, 15-40 down on serve in the final set, Osaka ran off four straight games to complete an improbable comeback on Rod Laver Arena in one hour and 55 minutes. 

"I think today was just a battle, like if I can just describe it in one word. For me, I feel like I'm very happy with myself for the way I overcame the match. I think maybe a year ago - definitely a year ago - I probably wouldn't have won this match. There are so many things that I was thinking about on the court that just would have blocked me from trying to win the match or trying to problem solve."

- Naomi Osaka

Earlier in the match, she rallied from 6-4, 2-0 down to force a final set in the first-ever meeting between the two Grand Slam champions.

"Overall, I think it was a pretty good match. We had a lot of great points," Muguruza said in defeat. "I felt, of course, a little bit disappointed being 5-3 in the third set up, having match points. It's never a good feeling losing a match that you feel you could have change in one second.

"But I left the court with a good feeling, very good feeling of this tournament in general."

Osaka hammered 11 aces and 40 winners over the course of the match to secure victory, overcoming Muguruza in blistering baseline rallies as the match wore on.

"I felt like I couldn't hit any ball at a slower pace or else she would immediately move me. I think that's why I made so many unforced errors, because I was sort of playing in a zone that wasn't comfortable for me," Osaka said.

"But I also think that's something that you get when you play against a Grand Slam champion. For me, that's where I feel I play the best because I feel like I'm pushed really hard."

Should the former World No.1 want to reach the semifinals, however, she'll next have to get past one of the most crafty players on tour — because as at long last, Hsieh Su-wei has finally reached a Grand Slam quarterfinal. 

In her 38th Grand Slam main draw appearance, Hsieh of Chinese Taipei moved into the elite eight thanks to a 6-4, 6-2 victory over No.19 seed Marketa Vondrousova of the Czech Republic.

Hsieh Su-wei celebrates making it into her first-ever Grand Slam singles quarterfinal at the 2021 Australian Open.

Photo by Getty Images

With two fourth-round losses at the major Down Under in her history, the third time was the charm for Hsieh as she eased past Vondrousova after 68 minutes of play.

The 35-year-old Hsieh, the current World No.1 in doubles, has now become the oldest player to make her Grand Slam quarterfinal debut in the Open Era.

The crafty veteran used her divine court craft to outwit the left-handed Vondrousova, and won 80 percent of her first-service points to bolster her carving and slicing. Vondrousova, the 2019 Roland Garros finalist, was hampered by 31 unforced errors in the match, almost double her winner count.

Hsieh let a big 5-2 lead slip a bit as she was unable to convert set point in that game, and Vondrousova powered her way to 5-4. But a love hold, punctuated by a whipping double-handed winner, allowed Hsieh to close out the set on her second time of asking.

Hsieh slammed a winning backhand to break Vondrousova in the first game of the second set, and the player from Chinese Taipei rolled from there, reeling off five straight games in total to get to 4-0.

Hsieh double faulted on her first match point at 5-2, but on her second shot, Vondrousova sent a return wide to give Hsieh a new milestone in her singles career.

While Osaka leads the head-to-head against Hsieh, 4-1, four of their matches have gone three sets — including a 5-7, 6-4, 6-1 win for Osaka in the third round in Melbourne in 2019. In that match, Osaka rallied from 7-5, 3-0 down.

"She's one of those players that, for me, if it was a video game, I would want to select her character just to play as her. Because my mind can't fathom the choices she makes when she's on the court. It's so fun to watch. It's not fun to play, but it's really fun to watch."

- Naomi Osaka on Hsieh Su-wei

Stat check: In the Open Era (since 1968), only four players have made more Grand Slam main-draw appearances than Hsieh (38 major main-draw showings) before reaching their maiden major quarterfinal – Tamarine Tanasugarn (45, 2008 Wimbledon), Silvia Farina Elia (44, 2003 Wimbledon), Elena Vesnina (42, 2016 Wimbledon), and Julia Goerges (41, 2018 Wimbledon).

"We all know she's a very good player. Anyone play her, they will get troubles. I not worry about it. She probably going to smash me on the court. I try to play my game, do my job, see what happens."

- Hsieh Su-wei on Naomi Osaka