An error-strewn Novak Djokovic kickstarted his bid for an 11th Australian Open and unprecedented 25th Grand Slam crown in unconvincing fashion on Sunday, dropping a set to "incredible" teenage qualifier Dino Prizmic.
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The Serbian superstar struggled to impose himself against the confident Croat on Rod Laver Arena before finally taming the 18-year-old 6-2, 6-7 (5/7), 6-3, 6-4 after a four-hour marathon.
While far from his best, the world No 1 showed no sign of the right wrist problem that hampered his build-up.
"Well, I started off very well for a 36-year-old guy. But, geez, when you think about it, I'm double his age," Djokovic said.
"Reality hit hard tonight," he added, smiling.
"But credit to him, he had an incredible game plan, he had an answer to everything.
"I had some good moments and other moments I wish I could have played better. Physically, I'm still finding myself on court."
Djokovic surged to the title last year with a three-set victory over this year's seventh seed, Stefanos Tsitsipas.
If he does the same again, he will pass Australian Margaret Court's all-time Slam record and join only Court (Australian Open) and Rafael Nadal (French Open) in winning 11 times at a single major.
Victory stretched his record at Melbourne Park to 90-8 as he reached the second round for a 17th consecutive year.
But he was troubled by Prizmic's speed and booming baseline play, which forced many uncharacteristic errors in a match many thought would be a cruise.
"He deserves every applause, every credit he gets," Djokovic said. "It's amazing to see someone so mature for his age – he handled himself on the court incredibly well.
HIS MOMENT
"This is his moment, honestly. It could have easily been his match as well. We are going to see a lot of him in the future."
The Croat is the current French Open boys' champion and he used the occasion to showcase his talent, undaunted by a Grand Slam main draw debut on Djokovic's most successful court.
He lost his opening service game, but held his next two before needing a medical timeout for a left thigh problem.
When he returned, Djokovic mercilessly moved him around the court to take the first set in 42 minutes.
Undeterred, the Croat, with his leg strapped, raced to a 3-1 lead in the second set, breaking Djokovic after he was given a time violation, then belting a glorious cross-court winner.
The Serb got back on level terms but it went to a tie-break, where Prizmic took charge, racing 6-2 clear. Djokovic saved three set points but not a fourth.
Djokovic pulled 2-0 clear in the third set, only for Prizmic to keep punching above his weight, winning the next three games.
But the defending champion found a new wind, saving two break points to hold for 4-3 before closing out the set, roaring in delight as he did so.
He broke the tiring teenager immediately in the fourth set before again needing to repel a fightback.
Battling to the end, Prizmic saved six match points before finally succumbing, with Djokovic next playing the winner of an all-Australian showdown between Marc Polmans and Alexei Popyrin.
SINNER STAYS FOCUSED AFTER WINNING START
Fourth seed Jannik Sinner got off to a winning start in his bid to claim his first Grand Slam title at the Australian Open as the Italian defeated unseeded Dutchman Botic van de Zandschulp 6-4 7-5 6-3 in the opening round on Sunday.
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Sinner, who enjoyed a strong finish to 2023 by reaching the ATP Finals title clash before guiding Italy to a Davis Cup triumph, was slightly off the pace after playing no competitive matches in the build-up to the year's first major.
A Melbourne Park quarterfinalist in 2022, Sinner grabbed a break in the opening game on Rod Laver Arena and battled to hold in the next before cranking up the pressure with searing winners on both flanks to take the first set.
World number 59 Van de Zandschulp went toe-to-toe with his opponent in the next set before Sinner sealed the decisive break for a 6-5 lead and comfortably doubled his advantage.
Sinner squandered four break points and then surrendered his serve to trail 2-0 as his forehand wobbled slightly in the third set but he responded superbly to close out the match and book a second-round meeting with Jesper de Jong or Pedro Cachin.
RUBLEV EDGES INTO SECOND ROUND
Andrey Rublev overcame a major wobble to beat Brazil's Thiago Seyboth Wild 7-5, 6-4, 3-6, 4-6, 7-6 (10/6) and reach the second round of the Australian Open on Sunday.
"For sure I will not forget this match," he said. "Thiago is a super-dangerous player, super-talented when in the mood."
The 26-year-old fifth seed suffered the indignity of being broken in his first service game but recovered from a 0-3 deficit to take the first set.
The Russian, who warmed up for the first Grand Slam of the year by winning the Hong Kong Open, was quickly into his stride in the second set, racing into a 5-1 lead and threatening to sweep his opponent aside.
He was pegged back by 78th-ranked Seyboth Wild but regained the initiative, putting away a volley at the net to move into a two-sets-to-love lead.
It looked only a matter of time before Rublev wrapped up the win but Seyboth Wild was not finished and a single break in the third set kept him in the fight.
The 23-year-old Brazilian, who upset Daniil Medvedev at Roland Garros last year, broke in the seventh game of the fourth set and levelled at 2-2 on a rapt Margaret Court Arena.
A nerve-jangling deciding set went with serve, with Rublev moving 6-5 ahead.
In the next game Seyboth fell to 0-40 under intense pressure from the Russian but he fended off those match points plus another to take the match to a tie-break.
The Brazilian raced into a 4-1 lead and then led 6-4 but Rublev stayed in the fight deep, winning the last six points and sealing the match with an ace.
He collapsed to the ground before letting out a guttural roar.
Rublev admitted that he relaxed in the deciding tie-break, believing he was heading out of the tournament.
"When I was losing 4-1, mentally I gave up and maybe that's what helped me in the end. I felt it's not my day but then I hit some good serves and good returns."