Steph Brantz and Brad Gilbert describe the road that got us to the 2017 Australian Open, with Roger Federer taking on Rafael Nadal. What do each of them need to do to be victorious? (2:08)

MELBOURNE, Australia -- Even by Friday night, when their dream Australian Open showdown was officially set, the foremost thought in Rafael Nadal's and Roger Federer's minds was only the challenge immediately in front of them.

The two tennis legends had just booked their ninth Grand Slam final date, but this one transcends the silverware as both men are playing for their legacies in what's easily the most important final they've ever contested.

And Andy Roddick, who was named to the International Tennis Hall of Fame earlier this week, would argue it goes even further than that: He insists this could be the most important Grand Slam final anyone has ever played.

Fellow Hall of Famer Pam Shriver doesn't disagree.

"This could be the match that a lot of people use to decide who really is the greatest of all time," Shriver said Saturday. "Does Roger win this magical one at 35? Or does Rafa add to his ridiculous head-to-head edge and narrow the gap?"

Rafael Nadal would be only two majors behind Roger Federer if he can take down the Swiss in the Australian Open final. Jason Heidrich/Icon Sportswire via Getty Images

Federer, who has won a record 17 Grand Slam titles, currently leads Nadal's 14, but that's about the only number on Federer's side.

Both he and Nadal have come back here from significant injury layoffs and are looking as impressive as they have in years. But at 35, Federer is five years older than Nadal.

If Federer wins Sunday's match, he stretches his major-title lead to four, and the chance of Nadal ever catching him looks appreciably worse considering the Spaniard hasn't won a Slam since 2014.

But if Nadal gets to 15 here, then the psychodrama could really be on full blast: Federer hasn't won a major himself since 2012, and Nadal would have a terrific chance to cut Federer's lead down to just one at the very next Slam, the French Open -- a tournament Nadal has won nine times.

Federer has won one title at the French, but it came in a year in which he didn't have to play Nadal.

Like Roddick and Shriver, Tennis Channel analyst Mary Carillo also believes the Greatest of All-Time debate remains open. And both Carillo and Shriver dismiss the idea that the major total should be the determinative factor if Federer finishes with a couple more than Nadal.

"I have said and argued with John McEnroe and Ted Robinson during our French Open telecasts for many years that you cannot anoint Roger Federer the greatest of all time if he isn't the greatest of his own time," Carillo said in Melbourne on Saturday. "And it's not just on red clay. Nadal has the edge on hard courts as well. Like in boxing, it's all about the matchup. When Roger is playing at his luminous best he has no need to worry about the other side of the net.

"But if he is playing Nadal, even his best is often not enough."

Federer has just two wins in eight Grand Slam finals against Rafael Nadal. Jason Heidrich/Icon Sportswire via Getty Images

That last line is the most damning argument against Federer.

Nadal has a 23-11 edge in their head-to-head rivalry, including a 6-2 lead in Slam finals. As Shriver says: "Rafa is so far ahead in the head-to-head if he wins tomorrow, to me 17 to 15 [majors] doesn't mean a whole lot. ... Rafa would also now have two career Grand Slams [two wins at every major]. Roger doesn't. And Rafa has played all of his career -- all of it -- in an era with Andy Murray, Roger and Novak Djokovic there the whole time. Roger snuck the first six or seven Slams of his career in before all that happened."

So why aren't more people already campaigning for Nadal to be considered best ever?

"People conflate [Federer's] beauty with supremacy and blur the line between high art and [Nadal's] impossible-to-ignore domination," Carillo says. "I think Roger Federer is the most stylish, elegant and gifted tennis player I've ever seen. Roger is all that is right in this tennis world. Rafa Nadal is his perfect rival -- powerful, explosive, gritty and gutsy."

If Nadal does win another Slam here or at the French, there's no guarantee Federer could pad his lead at his beloved Wimbledon anymore. Federer has seven titles at the All England Club, but even there, Nadal has a win against him. Nadal is 1-2 against Federer at Wimbledon, and his one win -- their epic 2008 final that went to 9-7 in the fifth -- is often called the greatest championship match ever played.

What has been surprising here in Melbourne is Federer, who is usually exceptionally careful with what he says. On Thursday he agreed that it should help him that he and Nadal haven't played a major final in a while. He said in hindsight, he believes Nadal snapped his title streak at Wimbledon in 2008 because he was still haunted by how Nadal "crushed me" in the French Open final a few weeks earlier.

For the ninth time, Rafael Nadal will face Roger Federer in a Grand Slam final. Michael Dodge/Getty Images

"If you're looking at that, it's better to have not played," Federer said. "I wasn't fighting the right way. I think that was the effect that the French Open loss left on me. Now it's a different time. A lot of time has gone by. I know this court allows me to play a certain game against Rafa that I cannot do on center court at the French Open."

Still, that Federer would volunteer Nadal has enjoyed a mental edge as he's about to play his nemesis again makes you wonder. Is that intimidation still in play?

Both Federer and Nadal have looked terrific these past two weeks. But Federer revealed during his five-set semifinal escape over Stan Wawrinka that he's dealing with an unspecified upper leg injury, too. If his movement is compromised at all, Federer will have trouble weathering Nadal's assault. Federer also admitted Wawrinka controlled the baseline against him more than he wanted. Nadal, whose booming forehand has been sensational here, is even better at that than Wawrinka.

Nadal literally went after every point in his five-set war with Grigor Dimitrov on Friday, showing a ferociousness Federer will have to match. Federer knows all this, of course. Whether he has the goods to hold off Nadal is another story.

Either man can win. Whoever does can further alter the Best Ever argument.

It looked all but settled once upon a time.

It isn't any more.