Daniil Medvedev stayed on track for a third Australian Open final in four years on Monday as Ukrainian qualifier Dayana Yastremska upset former champion Victoria Azarenka to surge into the quarter-finals.
They made their moves ahead of an evening session headlined by Spanish star Carlos Alcaraz, who is seeking to reach the last eight for the first time.
Russian third seed Medvedev was made to work hard by Portugal's Nuno Borges before winning 6-3, 7-6 (7/4), 5-7, 6-1 after more than three hours on Rod Laver Arena.
The 27-year-old will meet Polish ninth seed Hubert Hurkacz for a place in the last four.
"Before this match I was feeling 100 percent," said Medvedev, defeated by Novak Djokovic in the 2021 final and by Rafael Nadal the following year.
"But he made me run third set and that's why I missed a little bit too much. I was pretty dead to be honest. In the fourth set I managed to raise my energy levels."
Big-serving Hurkacz ended the dream run of French wildcard Arthur Cazaux 7-6 (8/6), 7-6 (7/3), 6-4 to advance to his first quarter-final at Melbourne Park.
Earlier, Yastremska fought off two set points in the first set and came from a break down in the second against two-time champion Azarenka to win 7-6 (8/6),6-4.
Her reward is a clash with unseeded Czech Linda Noskova, who went through when Ukraine's Elina Svitolina retired with a bad back while trailing 3-0 in the first set.
"I need to take a little bit of time to breathe because my heart I feel is going to jump out of my body," said Yastremska, who hammered Wimbledon champion Marketa Vondrousova in the first round.
"I always felt like I was running behind the train, but I think because I am a little bit of a fighter that's why I won this match."
Noskova, 19, barely broke a sweat to progress after former world number three Svitolina was unable to complete her match on Margaret Court Arena.
The 19th seed needed a medical timeout at 2-0 down in the first set, during which she received treatment for her lower back, and she pulled out after being broken for the second time on her return.
"I got a spasm, or I don't know exactly what it is, but like shooting pain in the first game, the last two points," said Svitolina. "Couldn't do anything, completely locked my back."
Noskova, ranked 50 in the world, is enjoying a breakout tournament, including a stunning win against world number one Iga Swiatek in the third round.
Spanish second seed Alcaraz has yet to be fully tested but has shown glimpses of his best form.
Speaking after Saturday's third-round match, when Chinese teenager Shang Juncheng was forced to retire, trailing by two sets, Alcaraz said he was "feeling great".
"Probably seven, eight (out of ten)," said the 20-year-old, giving himself marks. "It's a high note. But that's how I feel.
"I think I'm improving every day. Every match that I'm playing, I'm feeling better and better. Moving, hitting the ball, and, of course I'm getting used to this court as well."
The Australian Open is doubling up as a shootout for the number one spot and defending champion Djokovic has already laid down a marker, dropping just three games in his fourth-round match on Sunday.
German sixth seed Alexander Zverev takes on Britain's 19th-seeded Cameron Norrie later in a match that could go the distance, while China's 12th seed Zheng Qinwen faces Oceane Dodin of France.
