"It was a final of Herculean proportions."

It came after an exhausting five hours and 24 minutes of high-octane, nerve-shredding action, which made it the second-longest major final in history.

Few could believe what they were witnessing as the 35-year-old Spaniard dug deeper than deep to deliver one of the greatest performances of his career to edge ahead of long-time rivals Roger Federer and Novak Djokovic in the race for supremacy.

It was an even more stunning achievement given Nadal feared his career could be over as he struggled to overcome a foot problem last year.

"It is a goal that seemed utterly ludicrous in December when he didn't know whether his foot would be strong enough to be able to play at this Australian Open - or even to continue his career," BBC tennis correspondent Russell Fuller said on BBC Radio 5 Live.

"And then Covid struck before Christmas. In terms of what Nadal has overcome to win this 21st title, this is the best. It is surely the greatest triumph of his sporting career. History has been written in Melbourne."

Fellow BBC Radio 5 Live commentator Gigi Salmon added: "It's quite simply unbelievable. No player in the Open Era had ever won the Australian Open title from two sets down. The last time Nadal managed that feat was back in 2007.

"It is incredible to think what Nadal has achieved. The fact that he has reached 21 is truly, truly extraordinary. He fights, he scraps and he is once again a Grand Slam champion."

'I am proud to share this era with you' - Federer and Djokovic congratulate Nadal

There was no shortage of praise for Nadal following his achievement, though perhaps the messages from Federer and Djokovic are those that will mean the most.

While Federer missed the Australian Open through injury, Djokovic was deported from Australia on the eve of the tournament after losing a court bid to overturn his visa cancellation.

In a message on Instagram, Swiss great Federer said: "What a match. To my friend and great rival Rafael Nadal, heartfelt congratulations on becoming the first man to win 21 Grand Slam singles titles.

"A few months ago we were joking about both being on crutches...amazing. Never underestimate a great champion.

"Your incredible work ethic, dedication and fighting spirit are an inspiration to me and countless others around the world. I am proud to share this era with you and honoured to play a role in pushing you to achieve more - as you have done for me for the past 18 years.

"I am sure you have more achievements ahead but, for now, enjoy this one!"

Djokovic tweeted: "Congratulations to Rafael Nadal for [his] 21st Grand Slam. Amazing achievement. Always impressive fighting spirit that prevailed another time."

The Serb added: "Medvedev gave it his all out there and played with the passion and determination we have come to expect from him."

Three-time Australian Open champion Laver said: "Two AO crowns and 21 majors, given everything you have endured this historic victory is so special Rafa. It has been a privilege to watch you doing what you love."

Elsewhere, British tennis player Katie Boulter tweeted: "Goosebumps. My heart is so full. Never seen a guy who deserves it more. Forever a Legend."

Women's quarter-finalist Alize Cornet said her "idol" Nadal's triumph had moved her to tears - and 12-time Slam champion Billie Jean King praised the Spaniard's "grit, guts, spirit, & determination".

"What a comeback!" added the American.

'One of the greatest wins I've ever seen'

BBC Sport readers were also rubbing their eyes in disbelief throughout Sunday's finale.

"I can't believe it. One of the greatest wins I've ever seen," Alex Howarth messaged #bbctennis, while Georgie Heath said: "Honoured to have been alive during the reign of Nadal, Federer, Djokovic and moments like this are what it's all about".

A tweet from Khan Karn read: "Nadal's skill is arguably the best, alongside Federer and maybe Djokovic, but his resilience, heart, mental strength and character is the greatest bar none. No-one else could have pulled that off".

Sho added: "Ridiculous comeback from Nadal considering he's 35, just come back from a long injury lay-off, and playing against in my opinion the best player in the world currently. Superhuman."

British player Laura Robson summed it all up on BBC Radio 5 Live.

"I can't remember a more fun match to commentate on - that was such a privilege," said the former British number one.

On Nadal's win, she added: "I think this one tops it all. There were no expectations. I don't think anyone expected him to make the semi-final, let alone the final, never mind winning it.

"It is what I consider his best achievement and one that surprised us all. The way he came out of nowhere, to win it in this way from two sets down. It's a privilege to watch something like that."