Defending champion Aryna Sabalenka surprised herself with her toughness as she survived a scare to secure a spot in the Australian Open fourth round.

In a battle of the power hitters on Rod Laver Arena, the world No.1 clinched a hard-fought victory over Denmark's Clara Tauson, winning 7-6 (7-5) 6-4.

"That was a great battle, she played unbelievable tennis," Sabalenka said of world No. 42 Tauson.

"It was really tough to play against her today and I am super happy I was able to stay in the game and able to push myself to the limit and try my best to put the ball back on that side and try to get the win."

Friday morning's match started bizarrely with neither player able to hold serve until the eighth game, when Tauson finally cracked the mould for a 5-3 lead.

It wasn't that either player served that badly, but Sabalenka only managed to win 50 per cent of points on her first serves and a dismal 38 per cent on her second.

Sabalenka fired up and won her first service game then took a 6-5 lead but the Belarusian was left frustrated when Tauson, who won in Auckland en route to Melbourne, saved four set points.

In the tie-break, Sabalenka steamed to a 4-1 lead only for her rival to draw level before the defending champion conjured two big winners to seal the set.

Sabalenka got the jump in the second set, breaking Tauson for a 3-1 lead, but was still unable to shake the 22-year-old, whose previous best in Melbourne was a second round showing in 2022.

A fearless Tauson kept coming, breaking Sabalenka to level at 4-4 but in a marathon ninth game, the 2024 US Open champion exacted revenge to go up 5-4 and serve out for the match.

Sabalenka said she needed to draw on her mental strength to win the first set, and credited some hard times for building her resolve.

"During this match, I was thinking, 'Oh, my God, I'm really tough'," the 26-year-old said.

"It was so many really tough situations. I was just staying there. I was trying to put her under pressure. I was trying really hard.

"Yeah, I was thinking like, 'Wow, that's tough'.

"Over the years, I struggle a lot with different stuff. I think all of those difficult experiences make me really, really tough, tough person."

Hunting her third successive title, Sabalenka next faces teenaged Russian 14th seed Mirra Andreeva, who overcame Poland's Magdaleena Frech 6-2 1-6 6-2.