Novak Djokovic dropped a set in the first round of the Australian Open for the first time in 14 years but recovered to beat Jan-Lennard Struff.
Djokovic is going for an eighth title at Melbourne Park and is the clear favourite but he admitted he has focused on recuperation over the past week after an unusually-intense build-up that involved leading Serbia to the inaugural ATP Cup trophy.
He did much right in the night session on Rod Laver Arena and will not be overly concerned about the third set claimed by big-hitting German Struff, with Djokovic responding decisively in a 7-6 (5) 6-2 2-6 6-1 victory.
The second seed said: "I thought I started off well, I was a break up in the first set, he came back. Second set I played really well then he turned it around. Credit to him for fighting, he's a very powerful player."
Roger Federer remains cautious about his Melbourne hopes despite a convincing first-round win over Steve Johnson.
The 20-time grand slam champion had not played a competitive match since the ATP Finals in November and spoke ahead of the tournament about his concerns that he might be rusty.
There was little evidence of that as he breezed past American Johnson under the Rod Laver Arena roof, winning 6-3 6-2 6-2 in just an hour and 21 minutes.
Federer struck the ball very well but feels the real test of his form will come when he is put under pressure.
He said: "I just haven't played proper matches in many, many weeks, and a lot of guys, probably 95 per cent of the guys, are coming here with matches. So I'm not one of those guys. Now I have one. Best of five, too, which is even better.
"So I think for me really the first three rounds are key to get going, to get used to the pressure, or just to stay calm if you're down a set and a break or whatever it might be.
"This is sort of the unknown that can be a little bit scary at times. But today there was none of that because I broke early each set and was able to get on a roll, play freely after that. And also felt I had margin.
"Anything I was doing I felt like I had the game under control. That might not be the case in the next round, so I just think I have to be careful."
Last year's semi-finalist Stefanos Tsitsipas began his campaign in convincing fashion with a 6-0 6-2 6-3 victory over Italian Salvatore Caruso.
The 21-year-old was once again backed by Melbourne's large Greek community but admitted he has reservations about their noisy support.
"I really like that they come and support me because that gives me a lot of positives in my game," said Tsitsipas. "I don't really know why they want to go the extra mile some of the times.
"I think they should be a little bit more respectful to the opponents. I would describe it as a football field attitude, which doesn't really belong in tennis."
The first big shock came with a 6-3 6-7 (7) 6-1 7-6 (3) loss for 13th seed Denis Shapovalov against Hungary's Marton Fucsovics.
Shapovalov cut a frustrated figure throughout and was furious with umpire Renaud Lichtenstein for giving him a code violation for throwing, but not breaking, his racket.
The young Canadian, who has been tipped to break into the top 10 this season, said: "I think I played really nervous today.
"I was in really good shape, really good conditions going into the tournament. But I just played really tight.
"Obviously I feel like my game is there to beat any of the top guys, but of course there are so many great players out there. If I'm a little bit off, if I'm a little bit nervous, anyone could beat me as well.
"It's a really disappointing one, but there's nothing to do now except learn from it."
Eighth seed Matteo Berrettini eased to a 6-3 6-1 6-3 victory over wild card Andrew Harris, while Grigor Dimitrov recovered from a set down to defeat Juan Ignacio Londero.
But 25th seed Borna Coric was a first-round casualty, losing 6-3 6-4 6-4 to American Sam Querrey.
