After retaining the Australian Open to win his 20th grand slam singles title, Roger Federer revealed he felt like "a loss was coming" earlier in the tournament.

Federer beat Marin Cilic in five sets on Sunday to secure a record-equalling sixth Australian Open crown at the age of 36.

His progress to the final was largely stress-free and included a truncated semi-final triumph when Hyeon Chung was forced to withdraw through injury in the second set.

However, Federer was not high on confidence prior to his straight-sets victory over Tomas Berdych in the last eight.

"You can't explain it sometimes. It is just a feeling you get. It's like against Berdych, I felt like I'm probably going to lose this one," explained the Swiss in a news conference.

"I was not negative, but I just felt like I saw a loss was coming somehow. Not because I was not feel good or anything, I just felt like maybe Berdych is really feeling it."

Federer was 6-1 5-2 up on an ailing Chung in the semis before the South Korean retired.

"I didn't fall asleep very well after the Chung match," added Federer. "I think it surprised me. At this stage of a competition in the semis, to get a walkover, that was very odd for me. I couldn't fall asleep until about three in the morning.

"All of the next day I was already thinking about how should I play Marin, how cool would it be to win 20 [slams], but no, don't think of it, but how horrible would it be to lose it. I had it for over 36 hours, to be honest. It was a lot.

"I felt like the final came very quickly because of not dropping any sets and stuff, still having so many emotions left. I needed to probably work through these emotions this way. That's what made me nervous.

"But it's all good. I had a good start to the match. I think I lost the second [set] because of nerves, to be honest. It's all good. I like to care. It's good I can care about these matches."

The men's final was played under the roof of Rod Laver Arena due to extreme heat in Melbourne, with some pundits feeling an indoor match worked in Federer's favour.

"I was surprised to hear they had the heat rule in place for a night match," said the champion. "I never heard that before.

"When I arrived to the courts, I was totally ready to play outdoors. Half an hour before, we got the word that it's going to be indoors. For me, it doesn't change anything in the preparation, to be honest. I was ready for either."