Top-seeded Novak Djokovic overcame a couple of tumbles to the court and a series of energy-sapping baseline exchanges -- including one point that lasted 42 strokes -- to get back to the Australian Open quarterfinals for the first time since 2016 by beating No. 15 Daniil Medvedev 6-4, 6-7 (5), 6-2, 6-3.
Djokovic has won six of his 14 Grand Slam titles at Melbourne Park and is into his 10th quarterfinal at the hard-court tournament.
But he exited in the fourth round last year and the second round in 2017.
After edging Medvedev in a 3-hour, 15-minute struggle, Djokovic joked during an on-court interview: "Since I guess my next opponent is watching, I'm feeling fantastic. I've never felt fresher in my life."
At a later news conference, he was more circumspect about his preparation for Wednesday's quarterfinals.
"It was not the fall. It was not particularly the fall. It was just, you know, a little bit of fatigue, a little bit of back," he said. "Nothing major. But there are a couple of things that have surfaced, so to say, you know, after a match like this.
"We'll see tomorrow how the body reacts, but I'm confident I can recover and I can be ready for next one."
His next opponent is No. 8 Kei Nishikori, whose own fourth-rounder was even more grueling, going to a fifth-set tiebreaker and lasting 5 hours, 5 minutes.
Nishikori put away No. 23-seeded Pablo Carreno Busta 6-7 (8), 4-6, 7-6 (4), 6-4, 7-6 (8). Nishikori battled back from a two-set deficit and was trailing 8-5 in the tiebreaker when a contentious call changed the momentum and prompted an angry response from Carreno Busta.
Carreno Busta's shot clipped the net, and Nishikori reset to hit a backhand down the line after the ball landed near the doubles alley.
A line judge called Carreno Busta's shot out as Nishikori returned the ball down the line, and Carreno Busta was nowhere close to playing it. He challenged the decision, and Hawk-Eye showed Carreno Busta's shot hitting the line, so the point remained with Nishikori.
After arguing with umpire Thomas Sweeney, Carreno Busta lost the next three points and Nishikori sealed the match with an ace. After shaking hands with Nishikori, Carreno Busta threw his bag into the court before collecting it and yelling at the chair umpire as he left the arena.
Carreno Busta wasn't the only men's player to make a loud exit Monday.
Milos Raonic beat racket-smashing No. 4-seeded Alexander Zverev 6-1, 6-1, 7-6 (5) on his fourth match point to reach the quarterfinals for the fourth time Monday.
The big-serving Canadian had his serve broken in the opening game but responded by winning the next eight games to go up a break in the second set. After falling behind 4-1 in the second, Zverev had just about enough.
The 21-year-old German sat down in his courtside chair and destroyed his racket by whacking it against the ground eight times -- and then tossing it aside.
He was warned for racket abuse after the display and, after dropping the set two games later, he left the court and went to the locker room.
When he returned, he only dropped one point on his serve until the eighth game, but suddenly things went haywire again when he faced two match points. Zverev composed himself to save those two break points and led in the tiebreaker until Raonic went on a roll.
From 3-1 down, Raonic rallied to get to 6-4 and missed one more match point before finally converting.
The 2016 Wimbledon runner-up faces No. 28 Lucas Pouille next. Pouille beat No. 11-seeded Borna Coric 6-7 (7-4), 6-4, 7-5, 7-6 (7-2) to move into the quarterfinals.
He hadn't won a main-draw singles match in five previous trips to Melbourne Park, but he has quarterfinals experience at other majors including Wimbledon and the U.S. Open.
Pouille, who has a 0-3 record against Raonic, is being coached by Amelie Mauresmo, the 2006 Australian Open women's champion.
The Associated Press contributed to this report.