Defending champion Aryna Sabalenka blamed heavy balls and a slow court on Friday as she dropped four serve games in a row before "pushing to the limit" to keep her Australian Open hat-trick dream alive.
The world No 1 had to battle hard to beat Denmark's Clara Tauson 7-6 (7/5), 6-4 in the third round and reach the second week in Melbourne.
But her serving woes, which plagued her in the previous round, dogged her again in a roller coaster scrap that lasted more than two hours on Rod Laver Arena.
"Conditions are pretty heavy for servers," Sabalenka told reporters.
"It's not giving you that much advantage as usual. Balls are heavy. Courts are a little bit slower. You have to sometimes just put that serve in and play the rally."
Sabalenka had wobbled badly in her second-round win against Jessica Bouzas Maneiro, dropping her serve three times.
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On Friday it was even worse and Sabalenka was broken in the opening game by world number 42 Tauson.
It was the first of seven consecutive breaks between the pair – four by the top-ranked Belarusian – before Tauson belatedly held for a 5-3 lead.
That sparked Sabalenka into life as she finally held her own delivery to love then broke back again.
Sabalenka squandered four set points on the Tauson serve at 6-5.
On Sabalenka's fifth set point in the tiebreak she made no mistake, a rasping forehand winner putting her ahead.
"I think winning the first set – it was a very difficult set – gave me a little bit more mental strength that I can win this match even without serving my best," said Sabalenka.
She dropped her serve once more in the second set but fought back again until, at 4-4, the pair exchanged a succession of sizzling winners.
'GREAT BATTLE'
It resulted in the longest, most intense game of the match featuring seven deuces until Sabalenka secured the crucial break.
Sabalenka still had to save two more break points from the plucky Tauson, before clinching the match in 2hr 6min.
"That was a great battle," said Sabalenka.
"She played unbelievable tennis. It was really tough to play against her today. I'm just super happy that I was able to just stay in the game and I was able to push myself, honestly, to the limit.
"It was really important to get all of those breaks back. It could have gone either way."
Both players were seeking to extend their 2025 unbeaten streaks to eight matches after Sabalenka won the Brisbane International warm-up and Tauson clinched the title in Auckland.
In the end it was a 17th consecutive victory on Rod Laver Arena for Sabalenka.
Next up is either rising Russian teenage star Mirra Andreeva or Poland's Magdalena Frech.
Sabalenka is hunting down a rare hat-trick of consecutive Australian Open titles, a feat last achieved 26 years ago by Martina Hingis and only matched by four other women in history.
IMPERIOUS GAUFF ROLLS PAST FERNANDEZ
Coco Gauff extended her unblemished start to the season with a straight-sets win over Leylah Fernandez to roll into the second week.
The American world No 3, one of the favourites for the Melbourne title, eased to a 6-4, 6-2 third-round win on Rod Laver Arena against the 30th seed from Canada.
Gauff is yet to drop a set this season in eight matches having won all five of her singles at the season-opening United Cup, including a 6-3, 6-2 win over Fernandez which was the pair's only previous clash.
"I think it was harder because she knew what to expect, and I definitely think she played a little bit different today than at the United Cup," said Gauff, who is on an overall 12-match winning streak.
"Leylah is a great competitor, great player, great person so I knew today was going to be a tough match regardless of the result a couple of weeks ago."
Gauff, the 2023 US Open champion, lost to Aryna Sabalenka in the Australian Open semifinal last year, her best Melbourne Park performance to date.
She is drawn to meet the world No 1 and double defending champion at the same stage this year.
Before that the 20-year-old will face Belinda Bencic, who advanced when Naomi Osaka retired injured, for a place in the quarterfinals.
World number 29 Fernandez, the losing finalist in the 2021 US Open, was in the third round in Melbourne for the first time and found the precision of Gauff hard to handle.
The American stepped on the gas midway through the first set, breaking Fernandez to love.
A double break at the start of the second put Gauff in control, but serving at 3-0 she coughed up a pair of double faults to allow Fernandez a break back and a lifeline.
If Fernandez sensed a door opening, then Gauff immediately slammed it shut, breaking again for 4-1.
Serving for the match at 5-2, Gauff unleashed two searing backhand winners – one down the line and one across court – and sealed victory with an unreturnable lob in 1hr 16min.
INJURED OSAKA RETIRES
Two-time Australian Open champion Naomi Osaka retired with an injury during her third-round match against Belinda Bencic.
Osaka needed treatment on her stomach at 6-5 in a first set which she went on to lose on a tiebreak to her Swiss opponent, before shaking hands and leaving the court.
Osaka had a troubled build-up to the first Grand Slam of the year, retiring from the final in Auckland with an abdominal injury.
The Japanese star also revealed last week that she and her rapper boyfriend Cordae, the father of her daughter Shai, had split up.
But the former world No 1 came to Melbourne in confident mood, saying that her injury was improving.
"I'm pretty optimistic about playing my match. I mean, for sure I'm going to play my match," she said before the start of the tournament.
"I've been practising pretty well for the two days that I've been here, so it seems to be going good."
Osaka, a four-time Grand Slam champion, reached the third round of a Slam for the first time since the birth of Shai with fine wins over Caroline Garcia and Karolina Muchova.
But both went to three sets at Melbourne Park and clearly had taken a toll.
Osaka led 5-2 in the first set against Bencic before becoming hampered on her serve and in her movement, allowing Tokyo Olympic champion Bencic to draw level and take it to a tie break, which she won 7-3.
Osaka could not continue and left John Cain Arena waving to fans.
"It's not the way you want this match to end. I thought it was getting to be a good match," Bencic said.
"Hopefully she will be fine soon and can play well for the rest of this year."
Bencic will face Gauff in the fourth round.