There was a time when Nick Kyrgios couldn't bring himself to summon a single generous word for Novak Djokovic.
But watching him from the commentary box at Melbourne Park, the Australian now offers a rather different angle on his old avowed foe, declaring: "He's in the conversation for greatest athlete ever with what he's achieving."
Kyrgios was left swooning on Sunday at the manner in which the 36-year-old champion Djokovic kicked off his bid for an 11th Australian Open title, eventually subduing a precocious challenge from 18-year-old Croatian qualifier Dino Prizmic 6-2 6-7 (5-7) 6-3 6-4 victory after four hours.
"Seems like he's got every shot in the book out and showing us why he's the greatest player on the planet," sighed Kyrgios, making his commentary debut on Eurosport while admitting the incredible atmosphere on Rod Laver Arena made him desperate to experience it again back on court after his injury absence.
Of course, Kyrgios's 'bromance' with a rival he once couldn't stand has actually been going strong ever since they clashed in the 2022 Wimbledon final - but he was left genuinely astonished that Djokovic might actually be getting better than when the Serb downed him at SW19.
"He's getting older, his game's getting better, he's moving better… incredible. What do you have to do to beat him?" said Kyrgios.
"With no major injury, he definitely could play into his 40s.
"When you've achieved so much and become an icon in the sport, everyone wants you, they wanna take you down and they play their best tennis. So every single time Novak Djokovic goes out on to the court, it's not easy for him. That's even more credit to him.
"He has to keep studying these young players like Prizmic and keep adapting. Look how his game has adapted over the last five years. He just seems to rise to the occasion every single time.
"Never has a bad day; I suppose today would be one of his bad days - and he's still winning.
"He was telling me he's missing his family and if he wins this event, it's potentially another two weeks away from his beautiful family, but yet he's still got the same motivation to win. It's insane what he's doing."
Djokovic was told of Kyrgios's tributes after the match, and told Eurosport: "Great have him around... I don't know if he enjoys this kind of four-hour matches in the commentary box - but I wish I had his serve for some moments tonight!"
For Djokovic reckoned that it had been "a little bit like looking in the mirror" at the brilliant, resilient youngster Prizmic across the net, for whom he predicted a great future.
Kyrgios was impressed too. "Dino's got a bit of a swagger, he went toe-to-toe with the greatest of all-time. He's given Djokovic the longest grand slam first-round match of his career and that's pretty crazy for an 18-year-old.
"I like him! He's one of my favourite players after that performance.
"He should be super-proud of himself but Novak wore him down physically. When everyone else is getting tired, he's getting better.
"I could feel the energy out there, it's amazing - and I can't wait to get back healthy, to feel that once again."
