MELBOURNE, Australia -- Angelique Kerber remains the only Grand Slam singles winner in the Australian Open women's draw after surviving a frustrating fourth-round match.
For a while, though, it appeared that the former No. 1-ranked Kerber's progress may have unraveled against No. 88-ranked Hsieh Su-wei, a former No. 1-ranked doubles player with a double-handed grip on both sides.
With a mix of slices and chips, lobs and bunts, whippy half-volleys and wristy crosscourt ground strokes off both wings, Hsieh pushed Kerber to the extremes and unsettled her rhythm. The 2016 champion finally got a succession of breaks to take the second set and dominate the third in a 4-6, 7-5, 6-1 victory on Monday afternoon.
"Credit to her. She played an unbelievable match,'' said Kerber, who won the Australian and US Open titles and reached No. 1 in 2016. "I was feeling I was running everywhere. She was playing a lot of corners and drop shots. I was bringing a lot of balls back.''
After holding it together to improve her winning streak to 13 matches, Kerber faces U.S. Open quarterfinalist Madison Keys in the quarterfinals.
Keys returned to the quarterfinals here for the first time in three years with a 6-3, 6-2 win over No. 8-seeded Caroline Garcia. She is yet to drop a set at Melbourne Park and is averaging a brisk 62.5 minutes on court through her first four rounds.
Going into the fourth round, Keys had dropped only 14 games -- the second fewest among the women through three rounds, just behind Kerber's 13 games.
Top-seeded Simona Halep also advanced after successive first-round exits, beating Naomi Osaka 6-3, 6-2.
Halep, who could lose her No. 1 ranking if she doesn't win the title here, extended her record of not having lost a fourth-round match on hard courts at a Grand Slam since the 2013 U.S. Open -- she's 10-2 in round-of-16 matches.
She had considerably less trouble beating Osaka than her third-round match, when she needed 3 hours, 45 minutes and saved triple match point to beat Lauren Davis.
Halep will next face sixth-seeded Karolina Pliskova, who advanced with a 6-7 (5), 6-3, 6-2 win over No. 20 Barbora Strycova.
Pliskova clinched the match on her third match point when fellow Czech Strycova, who was serving, hit a backhand long.
Keys, the only American woman to reach the fourth round, said she feels like she's playing without pressure since returning from her wrist injury that forced her out of last year's Australian Open.
"I definitely realize how much l love it and how much pressure I put on myself'' in the past, she said. "Just being really happy to be back out here and not at home in a cast.''
Hsieh certainly made the most of her time in Melbourne, returning to the fourth round at a major for the first round in a decade. She lost to Justine Henin here in the round of 16 in 2008.
She has won two Grand Slam doubles titles and was ranked No. 1 in doubles in 2014. At 32, she was oldest woman still in the draw and had a career-high ranking of No. 23 in 2013. She's still in the doubles draw at Melbourne Park.
Information from The Associated Press was used in this report.