Tetchy title favourite Daniil Medvedev was pushed to the limit before reaching the last eight of the Australian Open on Monday but women's world number two Aryna Sabalenka crashed out after an epic that finished on the stroke of midnight.

Men's fourth seed Stefanos Tsitsipas survived a late-night fright to reach his third Australian Open quarter-final after a pulsating day of marathon matches, frayed tempers and searing heat at Melbourne Park.

A tetchy Daniil Medvedev reacts after a point against Maxime Cressy A tetchy Daniil Medvedev reacts after a point against Maxime Cressy Photo: AFP / MICHAEL ERREY

Tsitsipas was staring at defeat, trailing two sets to one before clawing back to beat the 20th seed Taylor Fritz 4-6, 6-4, 4-6, 6-3, 6-4 in 3hr 23min of classic punch and counter-punch tennis on Rod Laver Arena.

"It was an epic match. I gave everything out on the court today, I am very proud of myself with the way I fought," said the 23-year-old Tsitsipas who will now play Italian Jannik Sinner, who beat Australia's Alex de Minaur 7-6 (7/3), 6-3, 6-4.

Alize Cornet (top) celebrates her win against an exhausted Romania's Simona Halep Alize Cornet (top) celebrates her win against an exhausted Romania's Simona Halep Photo: AFP / Martin KEEP

Sabalenka lost a thriller that went to a final-set 10-point tiebreak as veteran Kaia Kanepi ended the Belarusian's hopes of a maiden Grand Slam title.

Second seed Sabalenka saved four match points before losing 5-7, 6-2, 7-6 (10/7), sending down 15 double faults as her serving yips that have plagued her throughout the Australian summer came back to haunt.

Alize Cornet (top) celebrates her win against an exhausted Romania's Simona Halep Alize Cornet (top) celebrates her win against an exhausted Romania's Simona Halep Photo: AFP / Martin KEEP

The unseeded Kanepi, 36, made it to the last eight in Melbourne for the first time, a stage she has reached at every other major over a Grand Slam career dating back to 2006.

"It was a really tough match," said Kanepi, who defeated three-time major champion Angelique Kerber in the opening round.

Back from the brink: Stefanos Tsitsipas Back from the brink: Stefanos Tsitsipas Photo: AFP / William WEST

The Estonian's reward is a quarter-final on Wednesday against seventh seed Iga Swiatek of Poland who battled from a set down to beat Sorana Cirstea of Romania 5-7, 6-3, 6-3.

Graphic charting the final stages of the Australian Open 2021 mens's singles competition. Graphic charting the final stages of the Australian Open 2021 mens's singles competition. Photo: AFP / John SAEKI

Earlier it took the petulant Russian men's world number two Medvedev 3hr 30min to subdue the unseeded American serve-volley specialist Maxime Cressy 6-2, 7-6 (7/4), 6-7 (4/7), 7-5 to set up a quarter-final against Canada's Felix Auger-Aliassime.

"It was long and it was not easy, the scoreline apart from the first set were all tough sets," said Medvedev, who clashed with the umpire, complained of bad luck and screamed "It's boring!" at Cressy's tactics.

Graphic charting the final stages of the Australian Open 2021 mens's singles competition. Graphic charting the final stages of the Australian Open 2021 mens's singles competition. Photo: AFP / John SAEKI

In the end, The US Open champion was mightily relieved to come through the most severe examination of his title credentials so far.

"If I didn't win the fourth set I would have been in a tough mental shape," he admitted.

French veteran Alize Cornet made the quarter-finals of a Slam for the first time in her long career.

Cornet ended her last-16 hoodoo in her 63rd Slam and will now face Danielle Collins for a place in the women's singles semi-final after upsetting former world number one Simona Halep of Romania 6-4, 3-6, 6-4 in energy-sapping daytime heat.

"It feels amazing. That battle I had with Simona today and the heat," said Cornet, who knocked out world number three Garbine Muguruza in round two.

"After 30 minutes we were both dying and we kept going for two-and-a-half hours."

Collins had an even longer battle, the American outlasting Elise Mertens of Belgium 4-6, 6-4, 6-4 across 2hr 51min of bruising action.

"It was really tough for me," said Collins, who made the semi-finals at Melbourne Park in 2019.

Men's ninth seed Auger-Aliassime overcame the 2018 Australian Open finalist Marin Cilic 2-6, 7-6 (9/7), 6-2, 7-6 (7/4) in 3hr 35min on John Cain Arena.

He joins Denis Shapovalov in the last eight to make it the first time two Canadian men have reached that stage at the Australian Open, and will now face Medvedev.

"It's amazing. It puts my belief even higher, I lost three times to Marin in the past, this is my first win against him," the Canadian said.

Sinner, the 11th seed, proved too strong for De Minaur to end Australia's last remaining hope in the men's singles with a 7-6 (7/3), 6-3, 6-4 win in 2hr 35min.

"It's very tough playing against Alex, especially in Australia," said Sinner, who joins compatriot Matteo Berrettini in the quarter-finals.