Daniil Medvedev admitted to loyal Australian Open fans "I would not be here" after he fought back to beat Finland's Emil Ruusuvuori from two sets down in a match that ended at 3:40 am on Friday.
The world number three, who took to the court late on Thursday, overcame the world number 53 by 3-6, 6-7 (1/7), 6-4, 7-6 (7/1), 6-0 in four hours and 23 minutes on a chilly Rod Laver Arena.
The second round match stretched well into the early hours even though tournament organisers added a day this year in an effort to curb late-night finishes.
"This one is going for sure to stay in my memory," the Russian told the few remaining spectators on the echoing court, bundled up against the cold.
"Honestly guys, I would not be here.
"Thanks for staying. If I would be a tennis fan... at 1:00 am I would be like 'OK, let's go home, were going to catch the end of the match on the TV. We're going to watch 30 minutes and then go to bed', so I guess thanks guys, you are strong."
The players were made to wait to get on court because the preceding match between Anna Blinkova and women's third seed Elena Rybakina lasted two hours and 46 minutes -- including an epic 22-20 tie-break won by Blinkova that stretched more than half an hour.
Earlier, women's world number one Iga Swiatek and men's second seed Carlos Alcaraz each played on the court for more than three hours, both coming out on top.
Medvedev, who will play Canada's Felix Auger-Aliassime in the third round, admitted that waiting to play the match in Melbourne had been "very tough".
"The toughest was the tie-break," said the two-time runner-up.
"With tennis, you never know when you have to eat, when you have to warm up and so here it was too early because I thought the match was going to be faster, the tie-break was going to be faster, so I was on the warm-up .
"You warm up five minutes, you rest five minutes but you stay so when I went on court I was exhausted already and it's not easy but he was better prepared in the beginning but I'm happy I managed to stay tough."
The former US Open champion, 27, said he hoped to get to bed by 6:30 am but admitted he would have to fit in time with his physio.
Australian Open organisers announced in October they were making the year's opening Grand Slam a 15-day event to limit late finishes after Britain's Andy Murray notably played until 4:05 am at the 2023 tournament.
Murray memorably asked during his epic five-set victory against Thanasi Kokkinakis: "Why are we playing at 3:00 am?"
