Defending Australian Open champion Novak Djokovic said it was like "playing myself in the mirror" after he came through the longest first-round Grand Slam match of his career against teenage qualifier Dino Prizmic.
Djokovic, chasing a record-extending 11th men's title in Melbourne, needed four hours and one minute to beat the 18-year-old 6-2 6-7 (5-7) 6-3 6-4.
Croat Prizmic, facing his childhood idol on his debut appearance at a Grand Slam, saved six match points before Djokovic, 36, secured victory.
"[He has] so much potential. He has everything that he needs and can still improve," world number one Djokovic said of his opponent, ranked 178th.
"The way he is mentally present on the court, I like it a lot. He never gives up.
"I felt like I was playing [against] myself in the mirror. He has no weaknesses, really."
Djokovic, who could achieve a record 25th Grand Slam singles title this month, later said he had felt "under the weather".
While the Serb will face Alexei Popyrin or Marc Polmans in the second round, Prizmic - crowned French Open boys' champion last year - has a bright future ahead on the evidence of his breakthrough performance on Rod Laver Arena.
Sunday's match surpassed Djokovic's previous longest in the first round of a major, which was a three-hour-57-minute encounter against Gael Monfils at the US Open in 2005.
Few could have anticipated the absorbing tussle which would develop after Djokovic took a straightforward first set.
But Prizmic hinted at what was to come when he broke Djokovic for the first time for a 3-1 lead in the second, before holding his nerve in the tie-break with his fourth set point.
That set up a rollercoaster third set, which Djokovic claimed by winning four successive games - but only after Prizmic had battled back with a double break from 2-0 down.
And even as the result began to appear a formality in the fourth set when Djokovic continued his run of games for a 4-0 lead, his teenage opponent refused to go quietly, breaking back before saving four match points in the ninth game to force the top seed to serve out victory.
"He deserves all the applause. He is an amazing player, he handled himself incredibly well on the court. This is his moment," Djokovic said.
"It could easily have been his match as well. He showed great mentality and resilience.
"I certainly want to be in his corner. So hopefully he will invite me, because he will make some big things in his career that's for sure."
'Panicking' Rublev wins in five sets
Andrey Rublev’s best Grand Slam result is reaching the quarter-finals on nine occasions
Fifth seed Andrey Rublev was "completely panicking" but survived a comeback from world number 78 Thiago Seyboth Wild to edge a five-set thriller.
The 26-year-old Russian, who will aim to reach his first major semi-final in 2024, won 7-5 6-4 3-6 4-6 7-6 (10-6) to set up a second-round meeting with Japan's Taro Daniel or American Christopher Eubanks.
"I started to have emotions in the fifth set. I screamed a couple of times. I was complaining. So [in] the fifth set when I started to feel panic [it] was tougher to manage emotions," said Rublev.
Rublev has at times struggled to contain his emotions on court. Against Carlos Alcaraz at the ATP Finals in November he hit himself so hard with his racquet that he drew blood.
His compatriot and good friend Daniil Medvedev also lost to Brazilian Seyboth Wild in five sets at last year's French Open - a factor Rublev said added to the pressure he felt.
"Daniil, Daniil. Almost all the fifth set, every game at least one or two times, I was thinking about what happened to Daniil because [in] the fifth set I was inside completely panicking."
Elsewhere, former semi-finalist Matteo Berrettini withdrew before his first-round match against Stefanos Tsitsipas because of a foot injury, meaning the Greek seventh seed will instead play Belgian Zizou Bergs.
American 12th seed Taylor Fritz also had to come through a five-set opener, fighting back from two-sets-to-one down to beat Argentine Facundo Diaz Acosta 4-6 6-3 3-6 6-2 6-4.
Compatriot Frances Tiafoe, seeded 17th, also progressed by beating Croat Borna Coric 6-3 7-6 (9-7) 2-6 6-3.
Croatia's 2018 runner-up Marin Cilic lost 6-1 2-6 6-2 7-5 to Hungarian Fabian Marozsan.
The Australian Open has been extended to 15 days this year in an attempt by organisers to avoid late finishes - with this its first Sunday start.
BBC